Skip to main content

Full text of "Anatomy of the brain and spinal cord"

See other formats


ANATOMY 



OF THE 



BRAIN AND SPINAL CORD 



w. 

ANATOMY 



OF THE 



BRAIN AND SPINAL CORD 



BY 



J. RYLAND WHITAKER, B.A., M.B.(LoND.) 

FKLLOW OF THE KOVAL COLLEGE OF PHYSICIANS, EDINBURGH 
LECTURER ON ANATOMY, SURGEONS' HALL, EDINBURGH, AND SCHOOL 

OF MEDICINE FOR WOMEN, EDINBURGH 
EXAMINKR IN ANATOMY, ROYAL COLLEGE OF PHYSICIANS, EDINBURGH. 



FIFTH EDITION. '- 




EDINBURGH: 
E. & S. LIVINGSTONE, 17 TEVIOT PLACE. 

1021. 



TO THE MEMORY 
OF THE LATE 

SIR JAMES ALEXANDER RUSSELL 

LL.D., M.A., B.SC., F.R.C.P.E., F.R.S.ED. 

3T|)i0 Kttle fflanual fe respectfully getoicateli 

IN REMEMBRANCE OF MANY KINDNESSES 



PREFACE. 

" This little book, first written whilst I was a student, 
still, as formerly, pretends to no originality. Its one 
aim is and always has been to present, in as clear and 
simple a manner as possible, an outline of the Central 
Nervous System to the student, who, for the first time, 
is brought face to face with this most intricate subject, 
and to furnish him, to the best of my ability, with those 
facts which he will find most useful in his future work, 
and which, let us trust, he will not have soon to unlearn." 
Although, owing to a sad bereavement, the book was 
out of print for nearly ten years, it has now reached a 
fifth edition. This, at my age, will, in all probability, be 
the last as far as I am concerned. In it my one endeav- 
our has been to keep the book as small as before. Any 
increase in length, apart from the inevitable addition of 
new matter, being chiefly due to the rewriting and 
extending of previous descriptions, with the object of 
rendering obscure passages easier to understand. New 
tables and recapitulations have also been given to serve 
for quick and easy reference. 

Both nomenclatures have been used. This under 
existing circumstances was unavoidable, if the book was 
to prove useful to those with whom it is likely to find 

vii 



viii PREFACE 

favour. The two groups of names have however been 
distinguished by difference in type, so that each one 
may choose for himself that which he prefers. 

My thanks are due to Messrs E. & S. Livingstone, 
the publishers; to Messrs M'Lagan & Gumming, the 
lithographers ; and to Mr Cathie, the artist ; but above 
all to Dr Alexander Walker and to Mr M'Donald 
Walker, for all the trouble they have taken in seeing the 
work through the press. 

SURGEONS' HALL, 
EDINBURGH, December 1920. 



TABLE OF CONTENTS. 

PAGE 

DEDICATION v 

PREFACE vii 

CONTENTS OF PLATES xiii 



SECTION I. 

SPINAL CORD, MEMBRANES, AND VESSELS .... 4 

Chapter I. 

MEMBRANES OF THE SPINAL CORD 4 

I. DURA MATER 5 

II. PIA MATER 7 

III. ARACHNOID 9 

CEREBRO-SPINAL FLUID n 

Chapter II. 

VESSELS OF THE SPINAL CORD n 

Chapter III. 

THE SPINAL CORD 14 

I. FISSURES OF THE CORD 16 

II. SPINAL NERVES 18 

III. WHITE AND GREY MATTER OF CORD ... 19 

i. WHITE MATTER 20 

Funiculi or White Columns .... 20 

Fasciculi or White Tracts 20 

Table of Funiculi and Fasciculi ... 28 

White Commissure 29 

Structure of White Matter .... 30 
ix . 



x TABLE OF CONTENTS 

Y ^ ^1- 

2. GREY MATTER 31 

Cornua 31 

Grey Commissure 33 

Neuroglia 34 

Nervous Constituents 35 

Vesicular Columns 35 

Structure of Nerve-cells .... 38 

IV. ORIGINS OF SPINAL NERVES 40 

SECTION II. 

DISSECTIONS TO EXPOSE PARTS OF BRAIN .... 46 

DISSECTION TO EXPOSE MEMBRANES 46 

DISSECTION TO REMOVE BRAIN 46 

DISSECTION OF VENTRICLES, ETC 48 

BRAIN, ITS MEMBRANES AND ITS VESSELS .... 40 

Chapter I. 

MEMBRANES OF BRAIN 50 

I. DURA MATER 50 

Falx Cerebri 52 

Falx Cerebelli 52 

Tentorium Cerebelli 52 

II. PIA MATER 54 

III. ARACHNOID 55 

IV. VENOUS SINUSES ........ 57 

Chapter II. 

VESSELS OF THE BRAIN 61 

I. ARTERIES 61 

II. VEINS 65 

III. LYMPHATICS 66 

Chapter III. 

SUBDIVISIONS OF THE BRAIN 68 

I. MEDULLA OBLONGATA ' 70 

1. Fissures of Medulla 72 

2. White Matter Areas, Columns, or Pyramids 

of Medulla 73 

3. Grey Matter of Medulla Ganglia ... 83 

Recapitulation 92 



TABLE OF CONTENTS xi 

PACT 

TI. PONS VAROLII 95 

1. White Matter of the Pons 98 

2. Grey Matter of the Pons 102 

III. CEREBELLUM 103 

1. Cerebellar Hemispheres and Vermis Cerebelli . 104 

2. Lobes of Cerebellum 106 

3. Peduncles of Cerebellum IOQ 

4. Medullary Vela . 112 

5. Grey Matter of Cerebellum 113 

Minute Structure of Grey Matter . . . 114 

6. White Matter of Cerebellum . . . . 116 
THE 4TH VENTRICLE 119 

IV. CEREBRUM 126 

I. EXTERIOR OR CORTEX OF CEREBRUM . . 127 

1. Fissures of Cerebral Hemispheres . . 127 

2. Lobes and Convolutions . . . . 130 
Structure of Cerebral Cortex ' . . . 144 

II. BASE OF CEREBRUM 147 

III. INTERIOR OF CEREBRUM 153 

I. VENTRICLES 155 

Lateral Ventricles 155 

The 3rd Ventricle ' 159 

Corpus Pineale or Pineal Gland ' . . 161 

The Septum Lucidum and 5th Ventricle 162 

Velum Interpositum . . . . 163 

Choroid Plexus 164 

Venae Cerebri Internae and Vein of Galen 164 

Great Transverse Fissure . . . 165 

II. BASAL GANGLIA 166 

Corpora Striata 166 

Optic Thalami 168 

Corpora Geniculata 1 70 

III. WHITE STRANDS 171 

Corpus Callosum 172 

Anterior, Middle, and Posterior Com- 
missures 174 

Fornix 175 

Internal and External Capsules . . 178 
Arterial Supply of the Capsules and of 

the Basal Ganglia . . . . 182 



xii TABLE OF CONTENTS 

PAGE 

TV. PEDUNCULI OR CRURA CEREBRI, etc. . . 182 

1. Tegmentum 18.5 

2. Crusta 189 

3. Substantia Nigra 190 

4. Corpora Quadrigemina . . . . 190 

5. Aquaeductus Cerebri or Aqueduct of 

Sylvius . 191 

6. Summary 192 

Mesial Section of Brain . . . 192 

Ventricles 194 

V. ORIGINS OF CRANIAL NERVES 197 

GENERAL SUMMARY 215 



SECTION III. 

i 

OUTLINES OF DEVELOPMENT ...... 232 

I. THE SPINAL CORD 233 

II. THE BR\IN . 238 

[NDKX . . 245 



ERRATA. 

Page 137. line 9. For "Centralis," read " Circularis." 
Page 137, line 19. For " Insula," read "Insulae." 



TABLE OF CONTENTS OF PLATES. 

I. Spinal Cord. 

PLATE i'AGE 

Arteries of iv 22 

Blood vessels of iv 22 

Columns of ii 8 

Commissure of iii 14 

Cornua of iii 14 

Development of xxxvi 238 

Division of i 4 

Filum terminale i 4 

Fissures iii 14 

Fasciculi of iv 22 

Funiculi of iv 22 

Grey matter of iii 14 

Grey matter of iv 22 

Grey matter of i 4 

Membranes of ii 8 

Membranes of i 4 

Nerves, spinal iv 22 

Deep origins ot . iv 22 

Nerves, Cells of . . v 34 

Neuroglia of v 34 

Parts of i 4 

Sections of ii 8 

Sections of .... .... iii 14 

Tracts of iv 22 

Tracts of xxxiii 222 

Vesicular columns of ....... iv 22 

II. Brain. 

Areas, Motor vi 50 

Motor x 64 



xiv TABLE OF CONTENTS OF PLATES 

PLATE 1-AGE 

Sensory vi 50 

Sensory x 64 

Vascular x 64 

Arteries ix 62 

Circle of Willis .... . ix 62 

Band of Giacomini xxvii 168 

Basal ganglia . xxvi 166 

Basal gangh'a xxviii 170 

Vessels of xxix 178 

Base of Brain xx 148 

Blood-vessels of Brain ix 62 

Brachia conjunctiva xi 72 

Brachia conjunctiva . . . . . . . xiv 96 

Pontis xi 72 

Capsules xxviii 170 

Vessels of xxix 178 

Caudate nucleus xxix 178 

Cerebellum xv 106 

Lobes and convolutions .... xv 106 

Structure xvi 114 

Cerebrum, Convolutions .... .xvii and xviii 130 

Crura of xi 72 

Section of xiv 96 

Fissures xvii and xviii 130 

Section, vertical xxix 178 

Structure xix 144 

Vascular areas x 64 

Choroid plexus xxiii and xxiv 160 

Choroid plexus xxv 164 

Cisternae vi 50 

Colliculi anteriores and posteriores ... xi 72 

Colliculi anteriores and posteriores . . . xxvi 166 

Commissures xiv 96 

Corpus callosum xxi 152 

Corpus callosum xxiii 160 

Anterior and posterior xxvi 166 

Convolutions xvii and xviii 130 

Crura Cerebri ...-..>... xi 72 

Corpora quadrigemina xxvi 166 

Decussations, Motor xxxiii 222 

Sensory xxxiii 222 

Development of Brain xxxvi 238 



TABLE OF CONTENTS OF PLATES xv 

I'LATE 1'AGE 

Divisions vi 50 

Fimbria xxvii 168 

Fascia dentata xxvii 168 

Fissures of Cerebrum xvii and xviii 130 

Fissures of Cerebellum xv 106 

Fissures of Medulla xi 72 

Foramen orForamina, 

Majendic vi 50 

Mouro ........ xxi 152 

Fornix xxiv 160 

Fornix xxvii 168 

Ganglia, basal ........ xxviii 170 

Ganglia, basal xxix 178 

Gyri of cerebrum xvii and xviii 130 

Interpeduncular space ..... xvi, fig. 59 114 

Interpeduncular space xx 148 

Insula, Isle of Reil xviii 130 

Lobes of cerebrum xvii and xviii 130 

Lobes of cerebellum xv 106 

Medulla ......... xi 72 

Nuclei of 4th ventricle xiii 90 

Sections of ....... xii 84 

Membranes vi 50 

Membranes vii 58 

Mesial section xxi 152 

Nerves, cranial ' xxxi and xxxii 200 

Nucleus candatus xxviii 170 

Nucleus candatus xxix 178 

Lenticularis xxviii 170 

Lenticularis xxix 178 

Ruber or red xiv 96 

Optic thalamus xxviii 170 

Optic thalamus xxix 178 

Optic nerves xxx 188 

Chiasma xxx 188 

Tracts xxx 188 

Olfactory tract xxx 188 

Parts of brain vi 50 

Pacchionian bodies viii 58 

Pendicles of cerebrum ...... xi 72 

I Vihmclues of cerebrum xi 72 

Section of . . xiv 96 



xvi TABLE OF CONTENTS OF PLATES 

I'LATE PAGE 

Peduncles of Cerebellum xi 72 

Pons vi 50 

Pons xi 72 

Sections ' xii 84 

Radiations optic xxx, fig. 80 188 

Restiform body xi 72 

Restiform body . xxx 188 

Sinuses, venous vii and viii 58 

Space interpeduncular xvi, fig. 59 114 

Space interpeduncular xx 148 

Striae medullares xi 72 

Structure of cerebellum xvi 114 

Structure of cerebrum xix 144 

Thalamus optic xxvi 166 

Thalamus optic xxviii 170 

Thalamus optic xxix 178 

Tracts, motor xxxiii 222 

Tracts, motor xxxiv 228 

Tracts olfactory xxx 188 

Tracts optic, xxx 188 

Tracts, sensory xxxiii 222 

Tracts, sensory xxxv 228 

Vascular areas of cerebrum x 64 

Velum interpositum . xxv 164 

Velum interpositum xxvii 168 

Ventricles xxii 158 

Ventricles xxiiiandxxiv 160 

Third ventricle xxvi 166 

Fourth ventricle xi 72 

Fourth ventricle nuclei xiii 90 

Venous sinuses vii and viii 57 

Veins, cerebral vii 58 

Vertical section xxi 152 

Vertical section xxix 178 

Willis, circle of ix 62 



ANATOMY 



CENTRAL NERVOUS SYSTEM. 






BRAIN AND SPINAL CORD. 

DEFINITION. By the term Nervous System we 
understand that group of tissues by means of which 
the several structures of an organism are brought into 
relation, conscious or otherwise, with each other and 
with their surroundings : in other words, that system 
which can conduct motor, sensory and other like 
impulses, to or from all parts of the body. 

CONSTITUENTS. The Nervous System is made up 
of two chief elements: (i) of a supporting connective 
tissue, called neuroglia nerve-glue; and (2) of nerve- 
cells with their processes, called neurones. The cells 
themselves are called neurone-bodies: their processes 
are called axones and dendrones, and the terminal 
filaments of the processes, dendrites (fig. 25, page 34). 

DIVISION. In man, as in all vertebrata, the Nervous 
System consists of two portions, the Cerebro-spinal and 
the Autonomic. The latter, the Autonomic System, 
composed of sympathetic and para-sympathetic, com- 
prises the numerous, small, scattered collections of 
nerve-ce'lls, called ganglia, with their branches of 

B 



THE CENTRAL NERVOUS SYSTEM 



communication and of distribution. The former, the 
Cerebro-spinal System, includes the rest of the nervous 
elements of the body, and is artificially divided into a 
central part, consisting of the Brain and Spinal Cord, 
and a peripheral part, composed of the several Nerves 
cranial and spinal which spring from the central 
portion. 






TABLE. 



(Sympathetic 
and 
Parasympathetic 



1. Central part the 

ganglia. 

2. Peripheral part 

the branches of 
communication 
and of distribu- 
tion. 



. 
2. Ccrcbro-spmal 



I- Central part. Cord. 

j N 
2 .Peripheralpart. 2 ; Spinal Nerves . 

We see then that the CENTRAL NERVOUS SYSTEM, 
the only part with which we are at present concerned, 
is divided into two portions, the Brain and the Spinal 
Cord. The one is enclosed within the bony walls of the 
cranium, whereas the other occupies the spinal canal. 
They form, however, one continuous whole, the line of 
demarcation between them being purely artificial, the 
part above the foramen magnum being called the Brain, 
the part below that foramen being called the Spinal 
Cord. 

The Brain and Spinal Cord are, moreover, each 
invested by three distinct membranes the Meninges 
which form additional protective sheaths around them, 
and help to support them in their respective cavities. 

They are both composed of two kinds of nervous 
substance known from their colour as the Grey and the 
White matter, but with this difference in their trrange- 



ment, namely, that in the brain the grey matter is 
situated chiefly on the outside, forming the bark, or 
cortex of the brain, while in the spinal cord the white 
matter is external, and the grey matter forms the central 
core or pith. The grey matter is mostly made up of 
nerve-cells, the white matter of nerve-fibres. 

Two groups of nerves called Cranial in the one 
case, Spinal in the other, spring respectively from the 
brain and spinal cord. Of these the latter arise by two 
roots named, from their positions, the anterior and 
posterior, and, from their functions, efferent and afferent, 
the efferent or anterior roots, carrying impulses from the 
brain : the afferent or posterior roots carrying impulses 
to the brain. 

We shall describe 1st the Spinal Cord with its 
membranes and vessels, and 2nd the Brain with its 
membranes and vessels. 



THE CENTRAL NERVOUS SYSTEM 



SECTION I. 



SPINAL CORD, MEMBRANES AND VESSELS. 

DISSECTION. To see the spinal cord and its membranes it will be 
necessary to open the vertebral canal. To do this, remove the 
muscles from the vertebral grooves, and saw through the laminse 
of the vertebrae on each side, close to their union with the pedicles, 
being careful, especially in the thoracic and lumbar regions, to 
direct the edge of the saw inwards. Carry the incision downwards 
as far as the lower end of the sacral canal, and upwards as high 
in the neck as may be convenient. Break through with the chisel 
any partially sawn arches, cut through the various ligaments, and 
remove the pieces of bone thus detached. Carefully clear away 
the connective tissue, veins, and fat covering the outer aspect of the 
dura mater. Snip through the articular processes with the bone 
forceps, and dissect out one or more of the processes of the dura 
mater which pass through the inter-vertebral foramina. Examine 
the outer surface of the dural sheath, and then slit it open in its 
entire length. 



CHAPTER I. 

MEMBEANES OF SPINAL COED. 

(Plate I. Page 4, and Plate II. Page 8). 

THESE membranes are, in many respects, identical 
with those of the Brain, and are therefore similarly 
named. They are the Dura Mater, the Pia Mater, 
and the Arachnoid. The Dura Mater is the most 
external covering, the Pia Mater is in close contact 
with the cord, and the Arachnoid forms a vertical 
partition between the others, dividing the space 
between them into two viz. the sub-dural and the 



KlG. 1. 



Mesencephalon 

Metencephalon 
Myelencephalon 



Pars ceivicalis 



Fasciculi 
of nerve roots. 



Pars dorsalis. 



Pars lumbalis. 



Pars sacralis, 
Conns medullaris 

Filum terminate. 




PLATE I. 
Fiss. mediana 
ant. 

Pia mater. 
i_] . Arachnoidea. 

%/*_ Dura 
mater. 



Epithelium. 

Fiss. mediana 
post. 



Spinal Cord. Membranes. 



Dura mater. 



Arachnoidea. 



Pia mater 



Linea 
splendens 



Opening for 

spinal netve 

roots. 



M c L |a A Cuununj. Edla r 



SPINAL CORD, MEMBRANES, DURA MATER 5 

sub-arachnoid. Thus we speak of the sub-dural space, 
meaning that between the dura mater and the arachnoid, 
and of the sub-arachnoid, or that between the arachnoid 
and the pia mater. For convenience we shall describe 
(i) the Dura Mater; (2) the Pia Mater; (3) the 
Arachnoid. 

I. THE DURA MATER. 

(Figs 2 and 3, Page 4 ; Figs 4 and 7, Page 8). 

The Dura Mater is the most external and the 
strongest covering of the Spinal Cord. It is a firm 
fibrous membrane which is continuous at the foramen 
magnum with the similar membrane which lines the 
cranial cavity. Enclosed in the spinal canal, it does 
not, however, form an endosteum to the bones, and in 
this respect differs from the cranial dura mater. Its 
outer surface has a pearly-white, shining appearance, 
and is separated from the walls of the spinal canal 
by fat, by loose areolar tissue, and by a plexus of 
veins. Slender fibrous bands, especially at its lower 
end, attach it closely to the posterior common ligament 
of the vertebrae. In extent the dural sheath reaches 
from the foramen magnum to the second or third 
piece of the sacrum, where it ends in a conical cul-de-sac. 
As you will see upon opening it, the cavity which it 
encloses is both much longer and much wider than 
the contained spinal cord, for, whereas this latter ends 
at the first or second lumbar vertebra, the cavity reaches 
to the second or third sacral vertebra, and there is, 
moreover, a considerable interval between the inner 
surface of the dura mater and the outer surface of the 
cord. Below the pointed termination of the spinal 
marrow conns medullaris the cavity of the dural 



6 THE CENTRAL NERVOUS SYSTEM 

sheath is occupied by bundles of nerve-roots called, 
from their likeness to a horse's tail, the cauda equina. 
In the midst of this bundle you will be able to pick 
out a slender, silvery-looking thread, the filum terminate 
or central ligament (fig. la, page 4). Continuous with 
the apex of the conus medullaris, this terminal filament 
runs down the middle line amongst the nerve-roots 
to the lower end of the dural cavity. There it pierces 
the dural sheath, and receiving an investment from it, 
descends to be attached to the back of the coccyx. 
Thus, we see that the dura mater forms a very loose 
covering to the cord, and we find, moreover, that it 
has a greater capacity in the neck and back than it has 
in the loins. Smooth and glistening on its inner 
aspect, it presents, on each side, a longitudinal series 
of rounded openings arranged in pairs, anterior and 
posterior, one for each spinal nerve-root (fig. 3, page 4). 
These roots, as they pass out to the inter-vertebral 
foramina, carry with them, besides their own sheath of 
connective tissue, a tubular prolongation of the dura 
mater which, in part, ensheaths the spinal nerves and 
their ganglia, and, in part, blends with the periosteum 
of the neighbouring bones (fig. 4, page 8). 

It is important to recollect that, although the 
spinal cord itself ends at the spot indicated viz. 
the first or second lumbar vertebra the dura mater, 
the arachnoid, and the cerebro-spinal fluid, extend as 
far as the second or third piece of the sacrum, so that 
injuries inflicted upon the spine as low down as this 
latter point may cause death by inducing inflammation 
of the meninges. 

MINUTE STRUCTURE OF THE DURA MATER. Under 
the microscope, you will find that the dura mater 



SPINAL CORD, MEMBRANES, PIA MATER 7 

consists of white fibrous and yellow elastic tissue 
arranged in longitudinal bands or lamellae, with 
flattened, branched, connective tissue corpuscles, 
clasping the bundles of fibrils. Both its inner and 
outer surfaces are smooth and covered with epithelial 
plates. Many lymphatics and blood - vessels are 
furnished to its substance. It is supplied by slender 
nerve-filaments derived from both the spinal and the 
sympathetic system. 

II. THE PIA MATER. 
(Figs. 2, 3, 4, 7, Pages 4 and 8). 

DISSECTION. After slitting open the dura mater, the first 
membrane you will see is the delicate arachnoid. Pierce it with 
a sharp-pointed blow-pipe and inflate, as far as you can, the sub- 
arachnoid space. Next, to expose the pia mater, remove a small 
piece of the arachnoid from any part of the cord, leaving it intact 
elsewhere. 

The Pia Mater is the delicate, highly vascular, 
fibrous membrane which so closely surrounds the 
spinal cord that it cannot easily be stripped off. Like 
the dura mater it furnishes sheaths to the roots of the 
spinal nerves. A distinct process or fold of it passes 
into a fissure, called the anterior median fissure, seen 
on the front of the cord. Other smaller septa penetrate 
the spinal marrow at various points, carrying with them 
blood-vessels and lymphatics for the nutrition of both 
its white and grey matter. The largest of these septa 
fills the fissure at the back of the cord called the 
posterior median fissure (figs. 4 and 5, page 8). It is 
not, however, a fold of pia mater, like that in the 
anterior median fissure, but consists of a strand of the 
supporting tissue of the spinal cord called neuroglia. 
If afterwards you compare the pia mater of the cord 



8 THE CENTRAL NERVOUS SYSTEM 

with that of the brain, you will find that the former 
is thicker, less vascular, and more adherent to the 
subjacent nervous tissue. 

The outer surface of the pia mater is comparatively 
rough, and has the three following structures connected 
with it: the linea splendens; the ligamentum denticu- 
latum ; and the septum posticum. 

1. The linea splendens (fig. 3, page 4) is the thickened, 
vertical, fibrous band seen along the anterior aspect of 
the pia matter. It is sometimes difficult to make out. 

2. The ligamentum denticulatum is, on the other hand, 
the well-defined structure (fig. 3, page 4, and fig. 7, 
page 8) which runs longitudinally on each side of the 
cord in the form of a scolloped or toothed, white band, 
with its serrated edge turned outwards. It helps to 
support the spinal marrow within its dural sheath. 
Reaching upwards as high as the medulla oblongata, 
it ends below at the pointed extremity of the cord, 
the conus medullaris. Internally, it is continuous with 
the pia mater, about midway between the lines of origin 
of the anterior and posterior nerve-roots. Externally, 
its outer margin forms a series of tooth-like processes 
denticulations about twenty-one in number, which are 
fixed to the inner surface of the dura mater, in the 
intervals between the points of exit of successive nerve- 
roots. The highest of these denticulations is attached 
opposite the margin of the foramen magnum, between 
the last cranial and first spinal nerve, and the lowest 
between the twelfth thoracic and first lumbar nerves. 
The ligamentum denticulatum thus partially divides the 
sub-arachnoid space into an anterior and a posterior 
compartment. 

3. At the back of the cord is another process or 



Fiss. mediana ant 
Lig. dentic. 



Fiss. mediana post. 



Epithelium FlG - 4. PLATE II. 

Dura mater. 



Pia mater. 

A rachnoidea. 
Spinal n. 




Subdural space. 

Crossed tactil 
Funiculus post. 
Spino-thalamic . 

Funiculus lot. 



Subarachnoid space 

and trdbeculae. 
Septum posticum. 



FIG. 5. f^ Uncrossed tactile 

.Fiss. mediana post. 



i 




Funiculus ant. 

N. spinalis. 

Fiss. antero-lat 



. i Fiss. postero-lat. 

Fiss. mediana ant. 



FIG. 6. 



Fiss. mediana ant. 




Fiss. mediana 
post. 



Collateral br. 
Fiss. postero-lat. 



Radix post. 



Membranes of Spinal Cord. 




SPINAL CORD, MEMBRANES, ARACHNOID 9 

partition the septum posticum (fig. 4, page 8) which 
crosses the sub-arachnoid space, and serves to connect 
the pia mater with the arachnoid. 

Below the end of the spinal cord, the pia mater, 
though, at first, retaining its tubular form, afterwards 
becomes suddenly reduced in size, and is finally 
prolonged as a sheath to the delicate thread-like 
continuation of the spinal cord, the filum terminate or 
central ligament (fig. la, page 4). Its glistening and 
silvery hue distinguishes this ligament amidst the 
surrounding bundles of nerve-roots. 

Lying between the pia mater on the one hand and 
the arachnoid on the other, but connected with both, 
is a quantity of delicate connective tissue, clothed with 
epithelial scales and arranged in the form of a spongy 
network, called the sub-arachnoid trabeculae (fig. 4, 
page 8). The spaces, lacunae or areolae, thus formed, 
contain the greater part of the cerebro-spinal fluid. 

MINUTE STRUCTURE OF THE PIA MATER. The pia 
mater consists of a basis of white fibrous connective 
tissue, the fibres of which are arranged in interlacing 
bundles. Both its surfaces are covered with epithelial 
cells. It supports a fine plexus of blood-vessels, and 
possesses a complete network of lymphatics. Its nerve- 
supply is probably derived from the sympathetic system. 

III. THE ARACHNOID. 

(Figs. 2 and 3, Page 4 ; Fig. 4, Page 8). 

The Arachnoid is an extremely fine and delicate 
membrane, and is, as its name implies, very like a 
spider's web. It has no nerves and no blood vessels, 
and thus differs materially from the other two. 

Surrounding the spinal cord and forming a cylindrical 



io THE CENTRAL NERVOUS SYSTEM 

partition between the dura mater and the pia mater, the 
arachnoid divides the space between them into two 
the sub-dural and sub-arachnoid, previously referred to. 
The sub-dural space is very narrow, for the outer surface 
of the arachnoid is in more or less close contact with 
the dura mater. The sub-arachnoid space, on the other 
hand, is much larger and contains the chief part of 
the cerebro - spinal fluid. It is crossed by the sub- 
arachnoid trabeculas which connect the arachnoid, with 
the pia mater. The arachnoid, moreover, forms tubular 
prolongations round both the upper part of the filum 
terminale and round the teeth-like processes of the 
ligamentum denticulatum. Similar coverings are also 
furnished to the roots of the spinal nerves as they 
pass outwards to the dura mater. When, however, the 
roots pierce that membrane, and when the teeth of 
the ligamentum denticulatum become attached to it, 
the epithelium of the outer surface of the arachnoid 
becomes continuous with the epithelium lining the 
inner surface of the dura mater, whilst the rest of the 
arachnoidal sheath blends with the perineurium of the 
nerves (fig. 2, page 4, and fig. 4, page 8). Thus we see 
that each spinal nerve-root receives a covering from all 
three membranes of the cord. It is stated, too, that 
the sub-dural and sub-arachnoid spaces, though they 
do not directly communicate with one another, are 
both continuous with the lymphatic plexuses which 
surround the spinal nerves. 

Sub-arachnoid Space. The spinal sub-arachnoid 
space extends from the foramen magnum to the second 
or third segment of the sacrum. The upper part of the 
space contains, besides the cerebro-spinal fluid, the 
spinal cord, the roots of the upper spinal nerves and 



SPINAL CORD, SPINAL VESSELS n 

the ligamentum denticulatum ; in the lower portion we 
have the upper half of the filum terminate and the lower 
long roots of the spinal nerves. 

Cerebro-spinal Fluid. The cerebro-spinal fluid, 
about 1 20 to 1 50 c.c. in quantity, is a colourless, clear- 
looking, alkaline liquid containing a little protein, 
albumen and globulin. It chiefly occupies the inter- 
stices of the sub-arachnoid trabeculae. By its means, 
probably, an equality of pressure is maintained upon 
the brain and spinal cord ; hence we find that any 
sudden disturbance of the fluid, such as would be 
caused by pressure on a spina bifida, at once gives rise 
to serious cerebral symptoms, such as convulsions and loss 
of consciousness. It may also be nutrient in function. 

MINUTE STRUCTURE OF THE ARACHNOID. The 
arachnoid consists of bundles of white fibrous tissue, 
interlacing with one another, and arranged for the most 
part longitudinally. Both its surfaces are covered by 
epithelial cells. Many authors regard the arachnoid as 
one of the layers of the pia mater, and describe the two 
together under the term pia-arachnoid. 

CHAPTER II. 

THE SPINAL VESSELS. 

(Fig. 18, Plate IV. Page 22). 

DISSECTION. Remove the spinal cord with its sheaths from the 
spinal canal by cutting through the spinal nerves at their exit 
through the inter-vertebral foramina, and snipping the bands of 
connective tissue which attach it to the posterior common ligaments 
of the vertebrae. Now examine the spinal vessels. 

(To understand this section read Chapter III. first.) 

i. Arteries. The arteries on the surface of the 
spinal cord are the anterior and posterior spinal. They 



12 THE CENTRAL NERVOUS SYSTEM 

are derived from the vertebral, inter-costal, and lumbar 
arteries, and their branches form a network within the 
pia mater. 

The ANTERIOR SPINAL ARTERY, formed above by 
the union of two branches arising one from each 
vertebral artery, runs, as a single trunk, along the front 
of the cord underneath the linea splendens. As it 
passes downwards, it is reinforced by a series of 
anastomotic branches from arteries in the neck and 
back. It ends below upon the filum terminale. 

The anterior spinal artery gives off branches to 
the spinal pia mater, to the roots of the spinal nerves, 
and to the anterior median fissure the cleft seen on 
the front of the cord. The branch to the anterior 
median fissure is called the anterior median artery. 
On entering the fissure, it gives off alternately right 
and left branches commissural arteries which are 
distributed to the corresponding right and left halves 
of the grey matter of the cord (fig. 18, page 22). They 
constitute a central or centrifugal set of vessels which 
supply all the grey matter, with the exception of the 
posterior horn and a small part of the anterior horn 
(fig. 1 8, page 22). The larger branches reach the 
adjacent white matter. 

The POSTERIOR SPINAL ARTERIES, two in number, 
run downwards, one on each side of the spinal cord, 
behind the line of origin of the posterior nerve-roots. 
They are derived from the same source as the anterior 
spinal arteries, and are joined by small branches which 
enter the intervertebral foramina along with the roots 
of the spinal nerves. They anastomose freely and send 
offsets into the vertical septum at the back of the cord. 
Together with the branches of the anterior spinal artery 



SPINAL CORD, SPINAL VESSELS 13 

they form a peripJieral or centripetal set of vessels, which 
enter the spinal cord at right angles to its surface. 
They are distributed to the white matter of the cord, 
though the larger branches also help to supply the 
grey matter (fig. 18, page 22). 

Thus we see that there are three vascular areas in 
the spinal cord (fig. 18, page 22). 

(1) A superficial area coloured brown, composed of 
the chief part of the white matter supplied by the 
centripetal group of vessels. 

(2) A central area coloured red, comprising all the 
grey matter, except the surface of the anterior horn and 
part of the posterior horn supplied by the anterior 
median artery centrifugal set. 

(3) An intermediate area coloured green formed 
in part by grey matter and in part by the adjacent 
white matter and supplied by both sets of vessels 
centripetal and centrifugal. 

The left-hand side of the same figure shows two 
areas, the one supplied by the anterior spinal artery 
coloured yellow ; the other by the posterior spinal 
vessels coloured blue. 

2. Veins. The veins of the spinal cord lie within 
the pia mater and have an anterior, a posterior, and 
right and left lateral trunks. Larger on the back than 
on the front of the cord, they form a fine plexus 
over its surface. Laterally, after being joined by veins 
from the bodies of the vertebrae, branches pass out 
with the spinal nerves through the inter- vertebral 
foramina, and open into the vertebral, inter-costal, or 
lumbar veins, according to the regions in which they 
occur. 

3. Lymphatics. There are no lymphatic vessels, 



14 THE CENTRAL NERVOUS SYSTEM 

properly so-called, in the nervous system, but there 
are lymph spaces round the nerve-cells peri-cellular, 
and round the blood-vessels peri-vascular. 



CHAPTER III. 
THE SPINAL CORD. 

The Spinal Cord or Spinal Medulla is the elongated, 
cylindrical column of nervous substance contained with- 
in the vertebral canal. It is composed of two kinds 
of nervous matter an outer cortical part, consisting 
principally of white nerve-fibres, and an inner grey core 
or pith, consisting chiefly of nerve-cells and their pro- 
cesses. Honey-combed throughout by a delicate 
supporting network or stroma of connective tissue, 
called neuroglia or nerve-glue, it is invested by three 
membranes, the meninges ; gives origin to thirty-one 
pairs of spinal nerves ; and is partially divided by 
anterior and posterior median fissures into two lateral 
segments, which are united across the middle line by a 
band of grey and white matter called a commissure, 
(for the meaning of which word see note at the end of 
this section). You have already seen that the spinal 
marrow is much smaller than the capacity of its bony 
case, so much so, that, in the adult, it occupies two- 
thirds only of the length of the spinal canal. About 
eighteen inches long, it reaches from the foramen 
magnum to the lower border of the first or second 
lumbar vertebra. Above, it is continuous with that part 
of the brain called the medulla oblongata or cranial 
medulla (fig. 1, page 4) ; below, it ends in a pointed 
extremity, the conus medullaris, from the apex of which 



Regions of Spinal Cord. 



PLATE III. 



Cornu ant. 




CERVICAL. F,G. 12 




a-""^ y Fasccuneatu,.^ ' ^Lissautr't 

X/ >^ Fascgraciiis. *><*. 



FIG. 9. 



Clarke's col 




DORSAL. Flc -13. ^Direct pyrt. 

Desc. 

antero-lat 
Asc. ant lat. 



Spino-thal. 
Ijat. cerebellar t. 




Fasc cuneatus. 7 Fasc gradfe. 



C. TOSSCa 

pyrt. 

~LJ3sau.fr s I. 



FJG. 10. 




Ani cornu 



Lat. 



Post cornu. 




LUMBAR. 

Asc. 
antero-lat. t 

Spino- 
thalamict/ \ y /f | \ (J^ Cnaed 

I. P.vrt. 

\^> ^~ Lissauer ' s t. 
Fas, cvneatvs' ^ graciUli 



FIG. 11 




Columns or Cornua. 



SACRAL. 

Gmoen, tra 



FIG. 15. 



-> / ft- Prepyr t. 

,^f\ ^17 -CnwMrf 
/o.vc ^rr/7/, . /^ ' 



Fasciculi or Tracts. 



' L|U A Ciuuain j. Kdmburgb 



is prolonged downwards a delicate thread-like filament, 
the filum terminate (fig. la, page 4). According to the 
regions of the spinal cord from which the several groups 
of spinal nerves take their origin, different portions of 
the cord have received special names, thus we speak 
of the cervical, thoracic, lumbar, sacral, and coccygeal 
portions, meaning thereby, not the regions of the spinal 
column in which these several groups of nerve-roots lie, 
but the parts of the spinal cord itself from which they 
respectively take their origins, quite apart from the 
position which the nerve-roots occupy in the spinal 
canal. Moreover, the spinal cord is further subdivided 
into segments a segment being a section of the spinal 
cord with its right and left nerve-roots. Now, as we 
have 31 pairs of spinal nerves, so also have we 31 
spinal segments. 

The spinal cord, moreover, presents two swellings 
or enlargements an upper one, the cervical enlarge- 
ment extending from about the third cervical to the 
second thoracic vertebra ; and a lower or lumbar 
enlargement which, beginning at the tenth thoracic 
vertebra, is largest opposite the twelfth, and then 
gradually tapers away to the pointed extremity of the 
cord. The connection between the increase of nervous 
substance in these two parts of the cord, and the origin 
of the large nerve-bundles given off to the upper and 
lower limbs respectively, is sufficiently obvious. . 

Filum Terminate. This filament is the atrophied 
remnant of the lower part of the embryonic spinal cord. 
It extends from the end of the spinal cord, viz. ist or 2nd 
lumbar vertebra, to the back of the coccyx. It is divided 
into an upper part, the filum terminate internum, before 
it pierces the dura mater, and a lower part, the filum 



16 THE CENTRAL NERVOUS SYSTEM 

terminate externum, after it has passed through that 
membrane. In the upper part of its extent, the filum 
terminate consists of a central canal with walls of grey 
and white matter, but in the lower part it becomes 
solid, and is composed of cells, of blood-vessels, and 
ultimately of mere prolongations of pia mater and of 
dura mater. 

NOTE. As long experience has taught me that many students are 
puzzled by the exact significance of the term commissure, it may be 
well to explain the word by means of a somewhat crude example. 
Suppose, then, that we have two white marble columns, right and 
left, each with a central core of grey marble. If we now, throughout 
their entire length, fasten the inner faces of these two columns 
across the middle line, about midway from before backwards, by a 
thin, vertical slab of white marble, and behind this, opposite to and 
continuous with the grey core, by a similar slab of grey marble, we 
might say that the two columns were united by a white slab or 
commissure, between the white parts of the columns, and by a grey 
slab or commissure between the grey portions. 

So with the spinal cord, it has a right and a left half, each 
composed of white and of grey matter. These are united across the 
middle line by a thin slab of white matter, at the bottom of the 
anterior median fissure, forming the anterior or white commissure ; 
behind this by a similar slab of grey matter, at the bottom of 
the posterior median fissure, this forming the posterior or grey 
commissure. 

We shall now examine (i) the exterior of the cord 
with its spinal nerves ; then (2) the interior. 

I. FISSURES OP THE CORD. 

(Figs. 4, etc., Plate II. Page 8). 

On both the anterior and posterior aspects of the 
spinal cord we see a median longitudinal cleft or 
depression, which penetrates some distance into the 
nervous substance and partially divides it into two 
lateral halves. These clefts are called the anterior 



SPINAL CORD, FISSURES 17 

and the posterior median fissures (figs. 5 and 6, page 8), 
and the transverse band, composed of white matter and 
of grey matter, which connects the two halves of the 
spinal cord across the middle line at the bottom of 
these fissures, forms the commissure of the spinal cord 
(See note page 16). 

1. The ANTERIOR MEDIAN FISSURE is the wider 
of the two, though in depth it extends through only 
one-third of the thickness of the cord. It contains a 
distinct fold of the pia mater, which conveys blood- 
vessels into the interior of the spinal marrow (fig. 4, 
plate ii. page 8). At the bottom of this fissure lies 
the transverse band of nerve-fibres, the anterior or 
white part of the commissural band already referred to 
(fig. 5, page 8). 

2. The POSTERIOR MEDIAN FISSURE, narrower but 
deeper than the anterior, is rather a septum than an 
actual fissure, for it does not, like the anterior, contain 
a fold of the pia mater, but is filled up by blood-vessels 
and by connective tissue neuroglia attached closely 
to the deeper layer of the pia mater. The posterior or 
grey commissure lies at the bottom of this septum 
(fig- 5> P a ge 8). Near the middle of this grey com- 
missure you will find the central canal of the spinal 
cord. 

3. In addition to these median fissures there are, 
on each side of the cord, two lateral longitudinal 
depressions, the positions of which are indicated by the 
lines of origin of the anterior and posterior nerve-roots 
(figs. 5 and 6, page 8). They are called the ANTERO- 
LATERAL and POSTERO-LATERAL grooves, though the 
antero-lateral is scarcely a distinct groove. They mark 
out the surface of each half of the cord into three 



i8 THE CENTRAL NERVOUS SYSTEM 

funiculi or columns an anterior, a lateral, and a 
posterior. The anterior column funiculus anterior 
lies between the anterior median fissure and the anterior 
nerve-roots ; the lateral column -funiculus lateralis 
between the anterior and posterior nerve-roots ; and 
the posterior column -funiculus posterior between the 
posterior nerve-roots and the posterior median fissure 
(fig. 5, page 8, and fig. 16, page 22). 

In the cervical region, close to the posterior median 
fissure, two additional slightly marked clefts can be 
made out, one on each side. They are the paramcdian 
and lateral dorsal suta, and will be noticed afterwards, 

II. SPINAL NERVES. 
(Figs. 5 and 6, Plate II. Page 8, and Fig. 16, Plate IV. Page 2). 

Along the sides of the spinal cord arise, as we have 
already seen, the several spinal nerves thirty-one pairs 
eight cervical, twelve thoracic, five lumbar, five sacral, 
and one coccygeal. Each nerve takes its origin, called 
its superficial origin or termination, by two roots an 
anterior or ventral and a posterior or dorsal springing 
respectively from the antero-lateral and postero-lateral 
grooves. These roots arise from the spinal cord by 
many slender twigs or fasciculi (figs, i and 3, page 4), 
and are enclosed in sheaths similar to those of the cord 
itself. They pierce the dura mater by two separate 
openings, one for each root (fig. 3, page 4). Except in 
the case of the first nerve, the posterior roots are the 
larger, and their fasciculi are more numerous and thicker 
than those of the anterior roots. The individual fila- 
ments of the fasciculi are, however, finer in the posterior 
than they are in the anterior roots. The posterior roots, 
moreover, become connected with a ganglion, or collec- 



'9 

tion of nerve-cells spinal ganglion before they join 
the anterior roots to form a spinal nerve (figs. 5 and 6, 
page 8). The anterior roots are motor, the posterior 
sensory in function, whereas the spinal nerves them- 
selves, formed by the junction of the roots, are called 
composite nerves, because they are composed of fibres 
some of which carry motor and other sensory impulses. 
With the exception of the first or highest, these 
nerve-roots are not attached to the cord opposite the 
vertebra below which they leave the vertebral canal, but 
at a higher level. This difference between the points 
of origin and the points of exit a matter of considerable 
clinical importance though slight in the cervical region, 
increases as we descend the cord, until, at its lower end, 
the nerve-roots form an almost vertical bundle, known 
as the cauda equina. In the upper part of the cervical 
region of the cord, a little in front of the posterior roots 
of the first six nerves, we see a series of nerve-filaments 
which soon unite to form a single trunk, which ascends 
and enters the foramen magnum. These filaments are 
the twigs of origin of the spinal part of one of the 
cranial nerves, called the spinal accessory. 

III. WHITE AND GREY MATTER OP THE 
SPINAL CORD. 

Transverse sections of the spinal cord similar to 
those represented in the figures on the plate opposite 
page 14, will demonstrate to you the interior of the 
cord and its subdivision into two lateral halves. They 
will show you distinctly the existence (i) of the white 
cortex, (2) of the central grey core, and (3) of the 
commissural band, composed of white matter and grey 
matter, which connects together its lateral segments. 



20 THE CENTRAL NERVOUS SYSTEM 

1. THE WHITE MATTER. 

Taking up such a section of the spinal cord and 
examining it with the naked eye, you will see, as we 
have just said, that the white matter forms the outer 
or cortical part of the cord, and surrounds the grey 
centre. This white matter arranged in a series of 
FUNICULI or COLUMNS gradually increases in amount 
from below upwards, being specially augmented in the 
cervical and lumbar enlargements. Compared with 
the grey matter, it is more abundant in the neck and 
back, but less so in the loins (figs. 8 to 1 1, page 14). 

i. Funiculi or COLUMNS and Fasciculi or TRACTS. 
Your attention, you will remember, has already been 
called to the fact that the exit and entrance of the 
nerve-roots subdivide each lateral half of the cord into 
three longitudinal white segments or columns namely, 
an Anterior, a Lateral, and a Posterior. Now each 1 of 
these columns or funiculi, thus mapped out on the 
surface by the nerve-roots, and limited on their deep 
aspects by the central grey matter, can be further 
broken up into smaller tracts or fasciculi of ascending 
and descending nerve-fibres, which have received special 
names and have special functions (figs. 12 to 15, page 14, 
and fig. 17, page 22). 

Fasciculi Tracts or Strands. To determine by 
actual dissection these various tracts or strands would 
be an impossible task. It has, however, been accom- 
plished by the study of the development and of the 
degeneration of nerve-fibres ; for " we may learn as 
much of the course of nerve-fibres in their birth as in 
their death, in their development as in their decay " 
(Gowers). Development teaches us that different tracts 



SPINAL CORD, WHITE MATTER, TRACTS 21 

or bundles of nerve-fibres acquire their white substance 
medullary sheath at different periods of their growth 
(See page 43), so that, in specially prepared specimens, 
we are enabled to pick out and trace these tracts or 
systems through successive sections of the cord. On 
the other hand, the study of physiology and of the 
selective action exercised by disease so analogous to 
that exercised by certain poisons affords equally 
valuable information, for to it we are indebted for the 
knowledge that, when a nerve-fibre degenerates in 
consequence of injury or disease, the proper nerve- 
substance is replaced by connective tissue, which, when 
treated with suitable staining reagents, behaves differ- 
ently from the surrounding undegenerated nerves. 

By the above and other means we can define, with 
more or less certainty, the following tracts or systems 
in the several white columns of the spinal cord (See 
Table, page 28). 

(a) Funiculus Anterior ANTERIOR COLUMN. In 
this column have been mapped out a median and a 
lateral division. 

(i) The median division the DIRECT PYRAMIDAL 
TRACT FASCICULUS CEREBRO-SPINALIS ANTERIOR 
fasciculus of Tiirck is a well-marked bundle of fibres, 
situated close to the anterior median fissure (fig. 17, 
page 22). It is a descending or motor tract, and is, 
as we shall afterwards see, a continuation of that part 
of the anterior pyramid of the medulla oblongata which 
does not decussate in the medulla; hence its name, 
direct pyramidal tract. It decreases in size from above 
downwards, but can still be traced as a distinct 
fasciculus to the level of the first lumbar nerve, though 
isolated fibres have been followed as far as the fourth 



22 THE CENTRAL NERVOUS SYSTEM 

pair of sacral nerves. Although the fibres of the direct 
pyramidal tract do not decussate in the medulla, you 
must note that, as they descend in the spinal cord, they 
do cross over at different levels to the opposite side of 
the cord, and through the grey matter of the anterior 
horn of that side, become connected with the corre- 
sponding anterior nerve-roots. 

(2) The lateral division of the anterior column 
FASCICULUS PROPRIUS ANTERIOR forming by far the 
larger part of the column, has been also called the 
anterior root zone, basis bundle, or anterior ground tract. 
It is mostly made up of short fibres, called association 
fibres, which connect together different segments of the 
cord. There are, however, two long strands in this part 
of the anterior column, the anterior and posterior 
longitudinal bundles, which, at this level, are blended 
together, but ultimately become distinct and separate 
strands. 

(b) Funiculus Lateralis LATERAL COLUMN. This 
well-defined column, marked off on the surface of the 
cord by the antero-lateral and postero-lateral grooves, 
and limited internally by the grey matter, is composed 
of the following eight distinct strands of fibres (fig. 12, 
page 14, and fig. 17, page 22). 

(i) CROSSED PYRAMIDAL TRACT. This tract 

FASCICULUS CEREBRO-SPINALIS LATERALIS occupies 
the posterior part of the lateral column, at a little 
distance from the surface of the cord. It is, as we shall 
afterwards see, the continuation downwards of the chief 
part of the anterior pyramid of the medulla oblongata 
of the opposite side ; hence the name, crossed pyramidal 
tract. This crossed tract is the principal motor tract. 
It exists in all regions of the cord, though it decreases 



Ant. nerve roots 
Ven tro-spino-tha la m 

Ant. med. fiss. - 
Dorso-spino-thalamic 



Funiculus ant. 
Funiculus lat. 
Funiculus post. 



Post. med. fiss. _ 
Post, nerve roots. 



FIG. 16 

Vesicular Columns. 




PLATE IV. 



Inner. \ Group of ant 
Lat. ) vesc. col. 



Mid vesc. col. 
Lat. vesc. col. 



Post. Vesc. col. 
7 or Clarke's col. 

Section of nerve fibres 
and Neuroalia 
Cells. 



Fasc 



long{ 



ant: 
post. 

Fasc. 
ventro-spino-cerebellar 

Spino-tectal 
Spino-tha lam ic 

Fasc prop. lat. 
Cornu comm 

Fasc 
dorso-spino-cerebellar 

Fasc cuneatus 
Fasc. gracilis 



Area of ant. spinal art 



I^eft commissural 
branch 



Peripheral branches 



Area of 
post, spinal art. 



FIG. I? 
Fasciculi. 




FIG. 18 
Vessels. 



Direct pyramidal tract 
Fasc cerebro-sptnalis ant. 

~asc desc. cerebello- 
spinalis ant. 

/ ^ ' / ^ 

7 \ 

..// 1 \ ^.Triangular (Helwey). 
Fasc proprius ant. 

^ ' \_Prepyramidaltrait 
or rubro-spinal 

Fasc cerebro-sptnalis lat. 
, I or crossed pyramidal 

Lissauer's tract. 



Comma tract 

Superficial ^ 

Oval j- bundles. 

Septo-marginal J 



Ant. spinal art. 



Ant. median art. 




1. Superficial area brown. 

2. Central ,, red. 

3. Intermediate,, green. 



V." I.Jn A Cunning. Edinburgh 



SPINAL CORD, WHITE MATTER, TRACTS 23 

in sectional area as we descend the cord, for its fibres 
constantly turn into the grey matter (figs. 12, etc., 
page 14). 

(2) The UNCROSSED LATERAL PYRAMIDAL TRACT 
(fig. 17, page 22), so called because it neither crosses in 
the medulla nor in the spinal cord, is composed of fibres 
which mingle with those of the crossed pyramidal tract. 
It is a direct motor strand from the cerebrum of the 
same side (fig. 93, page 222). 

(3) The PREPYRAMIDAL TRACT rubro - spinal, or 
Monakow's bundle (fig. 17, page 22), lies immediately 
in front of the crossed pyramidal tract. It is a crossed 
motor strand, which starts in a collection of nerve-cells, 
called the red nucleus, which is situated in the mid-brain 
(See crura cerebri, page 185). 

(4) The DIRECT CEREBELLAR TRACT, formerly so 
named from its connection with the cerebellum of the 
same side, is also known as the FASCICULUS SPINO- 
CEREBELLAR DORSALIS Or POSTERIOR. Extending 

upwards from the level of the second lumbar nerve, 
through the medulla to the cerebellum, it forms the thin 
lamina of nerve-fibres which separates the crossed 
pyramidal tract from the surface of the cord (fig. 17, 
page 22 ; fig. 93, page 222 ; fig. 96, page 228). It is an 
uncrossed ascending tract. Its fibres take their origin 
from a group of nerve-cells in the posterior horn of the 
spinal cord, called Clarke's column, the cells of which 
are connected with the posterior nerve-roots of the same 
side. This column carries those sensations from tendons 
and from muscles, which are concerned with the co- 
ordination of muscles and with the maintenance of 
equilibrium (pages 27, 28). 

(5) The ASCENDING ANTERO - LATERAL TRACT.- 



24 THE CENTRAL NERVOUS SYSTEM 

Gowers' tract (fig. 17, page 22) lies on the surface of 
the lateral column in front of the direct cerebellar tract. 
It is comma-shaped in section and extends forwards 
into the anterior column nearly as far as the anterior 
median fissure (fig. 17, page 22). Though formerly 
regarded as a single strand it, in reality, consists of at 
least three bundles: (a) the anterior or ventro-spino- 
cerebellar; (b} the spino-thalamic ; and (c) the spino-tectal. 
Gowers' tract starts from the cells of Clarke's column, 
and from other cells of the posterior horn, a little below 
the level of the dorso-spino-cerebellar tract. Although 
it most likely extends through all the regions of the 
cord, it first appears as a distinct strand in the lumbar 
segment only. Its constituent fibres can be traced to 
the opposite side of the brain (cerebrum or cerebellum) 
to that at which the nerve-roots enter the spinal cord. 
It is, therefore, a crossed sensory route, the crossing taking 
place in the spinal cord through the inferior sensory 
decussations (fig. 16, page 22 ; fig. 79, page 188). 

(6) The DESCENDING ANTERO - LATERAL TRACT 
FASCICULUS DESCENDENS CEREBELLOSPINALIS VEN- 
TRALIS Lowenthal's tract occupies about two-thirds 
of the antero-lateral column. It is closely associated 
with Gowers' tract and, like it, is a composite strand. It 
is connected with the vestibular division of the auditory 
nerve, hence the name, vestibulo-spinal tract. It sub- 
serves those reflexes from the ear which preside over 
equilibrium and over the co-ordination of muscles. 

(7) The OLIVO - SPINAL FASCICULUS Helweg's 
bundle forms a strand of nerve-fibres, triangular in 
section, and therefore sometimes called the triangular 
fasciculus, which lies at the ventral end of Gowers' tract. 
It begins above in the cells of the olivary body of the 



SPINAL CORD, WHITE MATTER, TRACTS 25 

medulla. Most of its fibres are descending, a few only 
being ascending. Its use is unknown. 

(8) The rest of the lateral column FASCICULUS 
PROPRIUS LATERALIS also called the mixed zone or 
lateral ground bundle, consists of fibres which have a 
short course, and which connect together different 
segments of the cord. 

Thus we see that, in the lateral column, there are the 
following tracts, the crossed and uncrossed pyramidal ; 
the prepyramidal ; the three cerebellar tracts two 
ascending Gowers' and the lateral cerebellar ; and one 
descending the descending an tero- lateral or vestibulo- 
spinal ; the olivo-spinal tract, and the mixed zone. 

(c) Funiculus Posterior POSTERIOR COLUMN. 
The arrangement of the strands in this column some- 
what resembles that in the anterior (fig. 17, page 22). 
Thus, especially in the cervical region, we find, close 
to the posterior median fissure, (i) a narrow band 
called the FASCICULUS GRACILIS or fasciculus of Goll, 
and (2) an external division named the FASCICULUS 
CUNEATUS or the fasciculus of Burdach. They are 
marked off on the surface of the cord by the para- 
median and lateral dorsal sulci (fig. 44, page 72). 

(1) The FASCICULUS GRACILIS Golfs tract in- 
creases in size from below upwards. It is best seen in 
the thoracic region, for at lower levels it is not distinct 
from the next bundle, the fibres of the two being inter- 
mingled. It is a direct afferent tract from the muscles 
and from the joints to the brain, its fibres being derived 
from the posterior roots of the lower spinal nerves. 

(2) The FASCICULUS CUNEATUS -fasciculus of Bur- 
dach also increases in size as it ascends. Its fibres 
are derived from the posterior nerve-roots of the upper 



26 THE CENTRAL NERVOUS SYSTEM 

spinal nerves. We shall presently trace them towards 
their ultimate destination (see posterior nerve-roots, 
page 4 1). 

These two parts of the posterior column Goll and 
Burdach are of considerable importance in the path- 
ology of locomotor ataxy, a disease of the posterior 
columns and of the posterior nerve-roots, in which there 
is loss of muscular sense or sense of effort, and con- 
sequently of co-ordination of muscular movements, for in 
these tracts travel fibres which are closely connected with 
that sense and with the mechanism of co-ordination. 
That the columns of Goll and Burdach conduct sensory 
impulses from the muscles, bones and joints is also 
proved by the fact that in whales, where the extrem- 
ities are not developed, these columns Goll and 
Burdach are rudimentary in comparison to what they 
are in animals with well-developed limbs. 

(3) Another tract, the POSTERO-MARGINAL, is a small 
zone which lies in this column round the tip of the 
posterior horn, separating the horn from the surface. 
It is often called Lissauer's tract (fig. 17, page 22), and 
its fibres, which come from the posterior roots, run for 
a short distance upwards and downwards in the tract, 
and then enter the grey matter. Lissauer's tract is 
sometimes described with the lateral column. 

(4) The rest of the posterior column FASCICULUS 
PROPRIUS POSTERIOR consists of fibres which vary 
much in length ; they are mostly association fibres 
between different segments of the cord. 

Several other minor strands have been described 
in the different columns of the cord, but are not of 
sufficient importance to detain us here. Some of them 
are named in the table, page 28, and are figured in 



SPINAL CORD, WHITE MATTER, TRACTS 27 

fig. 17, plate IV. page 22. It is well, however, to 
remember that the several tracts are not so definite as 
the figure would indicate for they overlap each other 
and with the ascending fibres we find descending inter- 
mingled, and vice versa. 

To sum up then, the pyramidal tracts direct, 
crossed, and uncrossed the prepyramidal, and part 
of the antero-lateral tracts are descending or motor 
strands ; on the other hand, the posterior column, the 
lateral cerebellar tract, and Gowers' tract are ascending 
or sensory strands The rest of the white matter 
chiefly consists of inter-segmental or association fibres 
often called endogenous which connect together the 
cells of different segments of the cord. 

COURSE OF MOTOR AND SENSORY IMPULSES IN THE 
SPINAL CORD. Motor impulses travel along the spinal 
cord by one or other of the following routes (i) either 
along the lateral column of the opposite side to that at 
which they left the cerebrum crossed pyramidal tracts 
superior motor decussation ; or (2) along the anterior 
column of their own side direct pyramidal tracts to 
cross individually at a lower level through the inferior 
motor decussations ; or (3) along a strand of fibres which 
neither decussates in the medulla nor in the spinal 
cord, but keeps to its own side throughout its entire 
course uncrossed lateral pyramidal tract. 

Sensory Impulses. Of these impulses (i) those from 
muscles and tendons and those from bones and joints, 
and those of a finer tactile nature, travel through the 
posterior columns of the same side to that at which 
they enter the spinal cord. They are uncrossed in the 
cord, but, as we shall afterwards see, are crossed in the 
medulla, forming the superior sensory decussation. 



28 THE CENTRAL NERVOUS SYSTEM 

On the other hand (i) crude sensations of touch and 
of pressure, and (2) sensations of temperature and of 
pain travel along the lateral and anterior columns of 
the opposite side to that at which the nerves enter the 
cord, they therefore have a crossed course in the cord, 
the crossing taking place not at one level, but at a 
series of different levels, through the inferior sensory 
decussations. Vaso-motor impulses, i.e. impulses which 
preside over blood-vessels, are conducted by the lateral 
columns (see table page 44). 

TABLE OF WHITE TRACTS OF THE SPINAL CORD, WITH 
DUPLICATE NAMES FOR REFERENCE ONLY. 

i. Fasciculus cerebro - spinalis anterior or 
ventralis ; Direct pyramidal tract ; fasci- 



w o 

C 'C 
g 4> 

3 c 
5 rt 



.!= 3 



culus of Tiirck ; anterior pyramidal tract ; 
antero-internal tract. 

2. Fasciculus proprius anterior ; basis bundle ; 
anterior root zone ; antero-external tract ; 



anterior root or ground bundle. 



(a) Dorsal or posterior or median longitudinal 
bundle. 



X G 
C 3 

< [IH 

(b) Ventral or anterior longitudinal bundle or 



tecto-spinal. 
Fasciculus cerebro - spinalis lateralis or" 

Crossed pyramidal tract. 
Uncrossed lateral pyramidal tract. 



3. Prepyramidal tract ; rubro-spinal ; Monakow's I " 

bundle. * Q 

~ 1 4. Fasciculus ascendens spino - cerebellar 
dorsalis or posterior ; tract of Flechsig ; 
lateral cerebellar ; direct lateral cerebellar. 

*O 

5. Fasciculus ascendens spino - cerebellar 
ventralis or anterior ; antero - lateral 
ascending ; Cowers' (i) ventro-spino-cere- 
bellar, (2) spino-thalamic, (3) spino-tectal. 



SPINAL CORD, WHITE MATTER, COMMISSURE 29 



*** I 

1\ 

'c 

9 



6. Fasciculus descendens cerebello - spinalis 

ventralis or anterior ; vestibulo - spinal 
tract ; antero-lateral descending ; anterior 
marginal ; Lowenthal's bundle. 

7. Olivo - spinal ; bulbo - spinal, triangular or 

Helweg's bundle. 

8. Fasciculus proprius lateralis ; lateral ground 

bundle, mixed zone. 
/ 1. Fasciculus gracilis; fasciculus of Goll ; postero- 

internal or postero-median strand. 
Fasciculus cuneatus ; fasciculus of Burdach ; 

postero-external strand ; posterior root zone ; 

posterior ground fibres ; ascending postero- 

lateral tract. 

Marginal zone, Lissauer's tract. 
Cornu commissural ; median triangular ; septo- 

marginal, oval bundle. These are mostly 

association fibres. 
Comma tract and superficial bundle. These 

are different names for groups of descending 

branches of the posterior roots in some cases 

mingled with endogenous fibres. 
. Fasciculus proprius posterior. 



"8s 

X U 

ss 



2. White Commissure. The two anterior white 
columns of opposite sides of the cord are, as we already 
know, continuous with each other across the middle 
line through a band of white fibres, the anterior or 
white commissure, seen at the bottom of the anterior 
median fissure (figs. 8, etc., page 14). The constitution 
of this commissure is too complex for an elementary 
work of this kind. Suffice it to say that it consists of 
decussating fibres, and of axis-cylinder processes and 
protoplasmic processes of the nerve-cells of the grey 
matter, of collaterals from different sources, and of 
neuroglia cells and their prolongations. 



30 THE CENTRAL NERVOUS SYSTEM 

MINUTE STRUCTURE OF THE WHITE MATTER. 
Besides blood-vessels and lymphatics, the white matter 
of these various columns of the spinal cord consists 
(i) of a supporting framework of ordinary connective 
tissue, and of a special kind of connective tissue called 
neuroglia, which will be fully described under the grey 
matter (page 34), (2) of medullated or white nerve-fibres 
running for the most part longitudinally, and (3) of 
non-medullated nerve-fibres which accompany the white 
nerve-fibres. 

The white nerve -fibres of the spinal cord are the 
axis-cylinder processes of nerve-cells, and have almost 
the same structure as peripheral nerves, consisting of 
a central core or axis-cylinder covered with a white 
sheath. In transverse section this core, though made 
up of a number of fibrillae, appears as a dark spot 
surrounded by a laminated white or medullary sub- 
stance called the medullary sheath (fig. 16, page 22). 
Usually, however, neither neurolemma nor nodes of 
Ranvier can be detected, though some hold that they 
are both present. 

Collaterals. In their course along the spinal cord, 
the axis-cylinder processes of the nerve-cells turn in 
at right angles to their direction, and, entering the grey 
matter, break up into fine brushlets of branches or 
dendrites. Moreover, as they travel along the spinal 
cord they give off, at right angles to their course, a 
series of side branches called collaterals which can be 
traced to different parts of the grey matter. These 
also end in tufts or brushlets of fine varicose fibrillae. 
All these brushlets ultimately terminate in little knobs, 
and according to some authorities do not anastomose 
with each other, nor with the neighbouring fibrillai, nor 



SPINAL CORD, GREY MATTER, CORNUA 31 

with the processes of nerve-cells, but merely form a 
beautiful plexus synapses around the body of the 
cells. Other authors, however, hold that they do unite 
with the terminal filaments of other nerve-cells. At the 
point where the collaterals are given off, the fibres 
usually have a small triangular enlargement. 

2. THE GREY MATTER. 
(Figs. 8, etc., Plate III. Page 14). 

The grey matter occupies the interior of the spinal 
cord, and is completely surrounded by the white 
substance. It forms two columns right and left 
extending through the entire length of the cord, one 
in each half. These two columns are united across 
the middle line by a vertical, transverse band of grey 
matter the posterior or grey commissure. In trans- 
verse section, therefore, the grey matter presents more 
or less the appearance of the capital letter H for it is 
arranged in two irregular crescent-shaped masses, the 
down strokes of the H, one in each lateral half of 
the section (figs. 8, 9, plate ill. page 14), and the 
transverse band of grey matter the cross-bar of the 
H which joins them together across the middle line, 
is the posterior or grey commissure previously men- 
tioned. Each grey crescent is semi-lunar in shape, 
having its horns cornua pointing, the one forwards 
and outwards, the other backwards and outwards, 
hence they are known as the anterior and posterior 
cornua. The convexity of each crescent looks inwards 
towards the middle line, whereas the corresponding 
concavity is directed outwards. 

i. Cornua. The ANTERIOR HORN of each crescent, 
irregular in outline, is, for the most part, shorter and 



32 THE CENTRAL NERVOUS SYSTEM 

thicker than the posterior, and arches forwards and 
outwards towards the place from which the anterior 
nerve-roots take their superficial origin. It does not, 
however, quite reach the surface of the cord, some 
white matter being interposed. It can be divided into 
an enlarged anterior part or head, a narrow part or 
neck, and a hinder part or base. 

The POSTERIOR HORN on the other hand, is longer, 
narrower, and more pointed than the anterior, and 
almost reaches the surface of the cord at the fissure 
along which the posterior nerve-roots take their super- 
ficial attachment. There it tapers to a point, called the 
apex cornu posterioris, which is capped by a stratum of 
rather clear-looking connective tissue and nerve-cells, 
known from its gelatinous aspect as the substantia 
gelatinosa of Rolando. Near its base the posterior 
horn, like the anterior, is somewhat constricted, forming 
the cervix or neck, while the slightly enlarged part 
between the apex and the neck forms the caput cornu 
posterioris. 

LATERAL HORN. The outer concave side of each 
crescent, slightly behind its centre, is formed of a net- 
work of fine fibres, which projects outwards into the 
white substance (fig. 16, page 22). This network, called 
the processus reticularis^ is best seen in the cervical 
region. Immediately in front of this process, and 
about midway between the anterior and posterior 
horns, lies a collection of grey matter the inter-medio- 
lateral tract lateral vesicular column which may be 
regarded as a lateral horn (fig. 16. page 22). Look for 
it especially in the dorsal region. 

If you now take a series of transverse sections from 
the different regions of the cord, and compare them 



SPINAL CORD, GREY MATTER, COMMISSURE 33 

together, you will find that the grey matter is relatively 
most abundant in the lumbar region, and least so in 
the cervical. Again, if you notice the respective sizes 
of the anterior and posterior horns of each grey 
crescent, you will see that they differ in different 
regions, for whereas in the cervical region the anterior 
horn is broad and the posterior narrow ; in the dorsal 
region, both are narrow, and in the lumbar region, both 
are broad (figs. 8, etc., page 14). 

2. Grey Commissure (figs. 8, etc., page 14). We 
have already seen that the convex sides of the two 
crescents are united across the middle line by a band 
of grey nerve-substance, forming the posterior or grey 
commissure which connects together the lateral segments 
of the cord. This grey band, placed nearer to the 
anterior than to the posterior ends of the crescents, 
consists of nerve-cells, of neuroglia-cells, and of trans- 
verse nerve-fibres. About its centre may 'be seen a 
small opening a section of the central canal of the 
spinal cord. This canal is the remains of the primitive 
medullary tube of the embryo, and extends throughout 
the entire length of the spinal marrow. Above, it 
expands into a wide, shallow, lozenge-shaped area 
the fourth ventricle of the brain ; whilst below, it 
enlarges, becomes T-shaped in section, and is prolonged 
into the filum terminate. It is lined by a layer of 
columnar cells, ciliated in the child, though not so in 
the adult. 

CONSTITUENTS OF THE GREY MATTER MINUTE 
STRUCTURE. To examine the minute structure of the 
grey matter you will require specially prepared micro- 
scopic sections. Such specimens will show you that 
there are two chief constituents of the grey matter, viz. 

D 



34 THE CENTRAL NERVOUS SYSTEM 

(i) a ground substance or stroma of ordinary connective 
tissue and of a special kind of connective tissue, called 
neuroglia, and (2) nervous elements nerve-cells and 
their processes, embedded in this stroma. 

I. Neuroglia (figs. 23 and 27, p. 34), already referred 
to under the structure of the white matter, is a delicate 
and peculiar kind of connective tissue which pervades 
both the grey and white substance of the spinal cord. 
It consists of cells, which are of two kinds ependyma- 
cells and neuroglia-cells (figs. 23 and 27, page 34). 

(1) The Ependyma- Cells are epithelial cells which 
line both the central canal of the cord and the various 
spaces in the brain called ventricles. In the spinal 
cord the processes of these cells extend radially from 
the central canal to the deep aspect of the pia mater. 
They form a distinct mesial septum on the posterior 
aspect of the cord (fig. 23, page 34). 

(2) The Neuroglia- Cells Cells of Deiters Spider 
cells Astrocytes are stellate, nucleated cells which 
vary much in size. They have numberless slender 
processes, long and short, which usually do not bifurcate, 
but which, after extending a variable distance from the 
cell, end free without anastomosing. 

The processes of neighbouring cells cross and recross 
each other, and form an intricate network throughout 
both the grey and white matter. Neuroglia is pretty 
evenly distributed through the grey and white substance 
of the spinal cord, but, upon the surface, beneath the 
pia mater, and around the central canal, it forms distinct 
layers, the latter being called the central grey nucleus. 
The substantia gelatinosa of Rolando is a similar 
accumulation of neuroglia, but contains many nerve- 
cells. 



FIG. 19. 

Netve cells of anterior comu 
of spinal cord. 



Nerve Cells and Neuroglia Cells:\ PLATE V. 




DendriUs 

or 

protoplamic 
processes. 



idol 

cells 

v>ith fibrillae 

in body of 

fells. 



SPINAL CORD, VESICULAR COLUMNS 35 

The function of neuroglia is to support and protect 
the delicate nerve -tissues. It is of special interest, 
clinically, being the seat of many of the inflammatory 
processes which affect the central nervous system. 

2. The Nervous Constituents of the grey matter 
are of two kinds : (i) Multipolar nerve-cells the bodies 
of the neurones occurring either singly (figs. 19, etc., 
page 34), or collected into groups called vesicular 
columns ; (2) Medullated and non-medullated nerve- 
fibres, which are branched and unbranched processes of 
the nerve-cells, and which either form distinct strands 
or traverse the grey matter in all directions. 

We shall consider (i) the groups of nerve-cells, and 
(2) their structure. 

Vesicular Columns (figs. 8, etc., page 14). The 
various groups of nerve-cells, seen in transverse sections 
of the spinal cord, are, you will readily understand, 
sections of columns of cells, which extend either through 
the whole length of the grey matter, or only through 
certain regions of it ; hence they are known as vesicular 
or ganglionic columns. They are best marked in the 
cervical and lumbar regions. 

(a) ANTERIOR VESICULAR COLUMN. The largest of 
these groups is situated in the fore part of the anterior 
cornu. It can be traced throughout the entire length 
of the cord, and is known as the anterior vesicular column, 
though it can be subdivided into two groups the one 
anterior or inner, and the other lateral (fig. 16, page 22). 
The lateral group is confined to the cervical and 'lumbar 
enlargements ; in the latter region, however, an additional 
posterior group, which lies behind the anterior, makes 
its appearance. 

Since it is from these groups of cells of the anterior 



36 THE CENTRAL NERVOUS SYSTEM 

horn that the anterior or motor nerve-roots spring, the 
entire collection has been termed the motor vesicular 
column, or motor ganglionic column. 

The cells of these columns exercise a trophic or 
nutritive influence on motor nerves and on muscles, for, 
as we shall afterwards see, there are two strata of cells 
presiding over the nerves and muscles : (a) an upper 
stratum the first trophic realm or upper neurones 
situated in certain regions of the brain-surface ; and (&) 
a lower stratum the second trophic realm or lower 
neurones the nerve-cells of the anterior horn. Now, 
in any injury to the cells of the upper stratum first 
trophic realm the muscles are paralysed and rigid and 
any atrophy which follows is by no means rapid, being 
due to disuse ; whereas, if the cells of the anterior 
vesicular column, lower stratum second trophic realm 
be injured, the paralysed muscles are flaccid and 
degenerate rapidly. 

(b} POSTERIOR VESICULAR COLUMN. The cells of 
the posterior horn are for the most part not arranged 
in distinct groups. At the base of the horn, however, 
near its inner angle, is a well-marked collection of cells 
variously known as POSTERIOR VESICULAR COLUMN, 
Clarke s column or dorsal nucleus (fig. 16, page 22). 
Though it is found along only the middle region ol the 
cord, from the level of the 7th cervical to that of the 
2nd lumbar nerve, it probably has representatives in all 
regions of the cord. It is a most important column for 
its cells, along with others of the posterior horn, connect 
the posterior or sensory nerve-roots : 

(1) With the CEREBRUM of the opposite side, through 
the spino-thalamic tract ; 

(2) With the CEREBELLUM, either of the same side, 



SPINAL CORD, VESICULAR COLUMNS 37 

or of the opposite side, in the one case through the dorso- 
spino-cerebellar tract ; in the other through the ventro- 
spino-cerebellar tract. 

(3) With the nuclei in the roof of the MID-BRAIN 
the anterior corpora quadrigemina of the opposite side 
through the spino-tectal tract. 

These three last-named tracts you will recognise as 
the three constituents of Cowers' tract. 

Injuries to the cells of the posterior horn induce 
sensory and trophic changes in the skin. 

(c) LATERAL VESICULAR COLUMN. A third group 
of nerve-cells, the nucleus of the intermedio-lateral tract, 
often called the lateral horn (fig. 16, page 22), lies at the 
base of the posterior cornu on its outer or concave side, 
within the column of grey matter of the same name. 
It can be distinguished in the dorsal and upper lumbar 
regions of the cord. Its cells are the spinal centres for 
white nerve-fibres rami communicantes which pass out 
from the spinal cord through the anterior nerve-roots 
into the autonomic system. They carry impulses to 
non-striped muscles and to glands. 

(d) MIDDLE VESICULAR COLUMN. This group of 
nerve-cells is placed near the centre of the convex side 
of each grey crescent. 

TABLE OF VESICULAR COLUMNS. 



(a) Anterior Vesicular 
Column. 



Internal Group. 
External Group. 
Posterior Group found in lumbar region. 



. ,, . / Clarke's Column, dorsal nucleus found 

(6) Posterior Vesicular ( 

from the 7th or 8th cervical to the and 
Column. 

lumbar nerve. 

(c) Lateral Vesicular < Lateral Horn found in the thoracic and 

Column. ( lumbar regions. 

(d) Middle Vesicular 

Column. 



3& THE CENTRAL NERVOUS SYSTEM 

STRUCTURE OF THE NERVE-CELLS. The nerve-cells 
or neurones of the grey matter of the spinal cord vary 
considerably in size, in shape, and in structure. 

Firstly, as to the shape and size. Most of the cells 
are multi-polar and stellate in transverse section, and 
have two sets of processes protoplasmic and axis- 
cylinder processes. The smaller cells measure 20 p. 
in diameter, the largest cells measure 60 to 130 p in 
diameter. Such cells are found in the anterior vesicular 
column, especially in its outer group. Similar cells 
also occur in Clarke's Column. In the posterior horn 
most of the cells are small and spindle-shaped, others 
are larger with long curved processes. 

Secondly, as to structure. Each cell has a distinct 
spherical or oval fib-dilated nucleus, a single nucleolus, 
and a centrosome. It has, however, no distinct 
nucleated sheath, differing in this respect from the 
cells found in the various ganglia throughout the 
body, e.g. sympathetic and spinal ganglia, which have 
a distinct fibrous capsule, lined by epithelial cells. 

The body of the cell Cytoplasm is permeated by 
a network of delicate fibrillae neuro-fibrill<e. These 
fibrilla:: extend into all the processes of the cell and 
carry impulses either to or from the cell. Two chemi- 
cally distinct substances, chromatic and achromatic, are 
found in the cells. The chromatic matter, when stained 
with methylene blue, appears as granules, stripes, cones, 
and blocks, called Nissl's granules (figs. 20, 21, 22, plate 
V., page 34). These granules are probably the nutritive 
material of the cell, for they are used up during its 
activity. The achromatic matter, on the other hand, is 
the essential protoplasmic constituent of the cell. On it 
the life and the activity of the cell depend. 



SPINAL CORD, NERVE-CELLS, STRUCTURE 39 

Processes of Nerve-Cells are, as we have said, of two 
kinds: (i) axis-cylinder processes axons or axones ; 
(2) protoplasmic processes dendrons or dendrones, 
with their terminal branches or dendrites. 

(1) The AXIS-CYLINDER PROCESSES are branched or 
unbranched processes of the nerve-cells, and are con- 
nected to the nerve-cell either directly, as seen in the 
motor type of cell, or indirectly through a plexus of 
fibres, as seen in the sensory type. Composed of many 
primitive fibrillae they, in many cases, soon acquire a 
medullary sheath, and become the axis-cylinders of 
nerve-fibres, which, after a longer or shorter course, end 
in the grey matter in fine brushlets of branches or 
dendrites. They are centrifugal processes, carrying 
impulses away from the cell. 

(2) The PROTOPLASMIC or GREY PROCESSES are a 
series of delicate ramifying branches which cross and 
recross each other in all directions (figs. 24 and 25, 
plate V., page 34). They are centripetal processes, 
carrying impulses to the cell. Through their relation 
to neuroglia and to blood-vessels, they may possibly 
subserve the nutrition of the nerve-elements. 

In the cells, the protoplasmic and axis-cylinder 
processes are in most cases continuous with each other, 
traversing the cells without interruption : their terminal 
processes, however, according to some authorities, do 
not anastomose with the processes of other nerve-cells, 
but are merely in contact with the nerve-elements. 
Others, however, hold that, though in their development 
or mode of origin, and in their nutritive or trophic 
power, the nerve-cells are undoubtedly separate and 
distinct units, it by no means follows that they are 
one and individual in their structure. From the above 



40 THE CENTRAL NERVOUS SYSTEM 

facts, if true, it follows (i) that though nerve-cells can 
receive and transmit nerve-motion, they do not generate 
nerve-motion, but are nutritive only ; and (2) that 
contact, and not actual continuity, is sufficient for the 
conduction of motor, sensory, and reflex impulses along 
the spinal cord. 

IV. ORIGINS OF SPINAL NERVES. 
(Fig. 1 6, Plate IV., Page 22). 

The several spinal nerves are, as you know, com- 
posite nerves, by which we mean that they contain both 
motor and sensory fibres. They each spring from the 
spinal cord by two roots, an anterior motor, coming from 
the antero-lateral groove, and a posterior sensory, from 
the postero-lateral groove. These attachments to the 
cord are called the superficial origins or terminations 
of the nerves, as distinct from the deep origins or 
terminations the nerve-cells in the grey matter to or 
from which the nerve-roots can be traced. 

(i) The ANTERIOR NERVE-ROOTS Efferent or Motor 
Roots. Most of the fibres of these roots come from 
the nerve-cells of the anterior and lateral horns their 
deep or sub-cortical origins of the same side (fig. 16, 
page 22). The cells from which they spring are called 
root-cells, and the several bundles of white fibres, which, 
in sections of the cord, can be seen passing through the 
peripheral white substance to the antero-lateral grooves 
their superficial origins are the axis-cylinder pro- 
cesses of these cells. Other fibres of the anterior roots 
come from cells in the opposite anterior horn, and are, 
by means of collaterals and dendrites, brought into 
relation with the cells of the posterior horns. 



SPINAL CORD, SPINAL NERVES, ORIGINS 41 

(2) The POSTERIOR NERVE-ROOTS Afferent or 
Sensory Roots before reaching the spinal cord, pass 
through the spinal ganglion, their first primary station or 
origin, in which there are unipolar nerve-cells. At a little 
distance from the cells, the pole, or axis-cylinder process, 
bifurcates in a T-shaped manner, one limb of the T 
becoming the distal, the other the central end of a 
nerve-fibre of the posterior root (fig. 5, page 8). The 
central processes enter the cord in two sets, a mesial set, 
which forms the chief part of the posterior column, and 
is mostly made up of the fasciculus of Goll and the 
fasciculus of Burdach, and a lateral set, which forms 
the marginal zone Lissauer's tract. On entering the 
spinal cord all the fibres, mesial and lateral, at once 
divide into ascending and descending branches, which 
give off collaterals to different parts of the grey matter 
(fig. 6, page 8). The descending branches after a short 
course turn at right angles into the grey matter, and 
end free in little tufts of fine filaments. The ascending 
branches of Lissauer's tract lose themselves in the 
substantia gelatinosa of Rolando. Others belonging 
to the column, after a long, short, or intermediate course, 
also enter the grey matter, but, the ascending branches 
of the fasciculus of Goll and the fasciculus of Burdach 
do not enter the grey matter of the spinal cord, but reach 
the medulla, and end in the cells of the nucleus gracilis 
and cuneatus. From these nuclei new relays of fibres 
take their origins, and crossing the middle line in the 
superior pyramidal or superior sensory decussation (see 
page 88), travel upwards through the medulla and 
through the pons to the opposite side of the cerebrum. 

In the lower part of the cord, the ascending branches 
constitute the fasciculus of Goll only. They are derived 



42 THE CENTRAL NERVOUS SYSTEM 

from the sacral, lumbar, and lower thoracic nerve-roots. 
At higher levels, however, the column of Goll is pushed 
towards the mesial plane by the entrance into the cord 
of fibres derived from the upper thoracic and cervical 
nerve-roots, which now constitute the fasciculus of 
Burdach. Hence it follows that there is no real dis- 
tinction between these two parts of the posterior column 
Goll and Burdach, they are one in function and in 
constitution, differing merely in the length of their 
fibres, the column of Goll being composed of fibres 
which enter the cord below the level of the 8th thoracic 
nerve, the column of Burdach of those which enter 
above that level. The tracts of Goll, therefore, convey 
impulses from the lower limbs and from the trunk, the 
tracts of Burdach from the upper limbs and from the 
head and neck. Besides the fasciculi of Goll and 
Burdach, two other strands enter the spinal cord 
through the posterior nerve-roots. These are the 
lateral cerebellar tract and the three constituents of 
Cowers 1 tract. On entering the cord all the fibres 
of these tracts pass at once into the grey matter of 
the posterior horn and end amongst its cells. These 
cells, in their turn, give origin to new groups of 
nerve-fibres, of which the lateral cerebellar or dorso- 
spino-cerebellar tract ascends at once to the cerebellum 
of the same side ; the three constituents of Gowers' 
tract, however, cross the middle line at various levels, 
through the inferior sensory decussations, and ascend in 
the lateral and anterior columns of the opposite side to 
that at which the corresponding nerve-roots entered the 
spinal cord. Thus we see that the tracts of Goll and of 
Burdach, and the three constituents of Gowers' tract 
reach the brain on the opposite side to that at which the 



SPINAL CORD, SUMMARY 43 

nerves enter the spinal cord, but with this difference, 
that the one set decussates in the medulla, the other in 
the spinal cord, forming respectively the superior and 
inferior sensory decussations. 

SUMMARY. To sum up, then, we have the spinal 
cord presented to us as an elongated mass of nervous 
substance, consisting of white and grey matter ; in- 
vested by three membranes ; having two distinct 
enlargements; giving origin to thirty-one pairs of 
spinal-nerves ; nourished by spinal vessels, and divided 
by anterior and posterior mesial fissures into two 
lateral segments, each with three sub-divisions funiculi 
or columns which can again be mapped out into 
numerous fasciculi tracts or systems of varying 
significance. 

Again we see that whereas formerly the spinal cord 
was regarded as made up of two distinct elements 
nerve-fibres and nerve-cells we must now consider that 
it consists of one nerve-element only the neurone the 
nerve-cell with its protoplasmic and axis-cylinder pro- 
longations. These neurones are arranged in tiers or 
columns, and are connected together by their proto- 
plasmic and axis-cylinder processes and collaterals. 
These facts have important bearings on the physiology 
of the spinal cord. 

The following Tables will be found useful for 
reference : 

TABLE OF THE ORDER IN WHICH THE SEVERAL TRACTS OF 
WHITE MATTER RECEIVE THEIR MEDULLARY SHEATHS. 

1. Anterior and posterior nerve-roots and commissural fibres of 

the grey matter. 

2. Fasciculus proprius of the anterior, of the lateral, and of the 

posterior columns. 

3. Burdach's column and Lissauer's tract. 



44 



THE CENTRAL NERVOUS SYSTEM 



4. Coil's tract. 

5. Lateral cerebellar tract. 

6. Gowers' tract. 

7. Crossed and direct pyramidal tracts, which in man get their 

medullary sheath at birth. 

8. Helweg's tract. 



RULES TO DETERMINE THE LEVELS OF THE ORIGINS OF THE 
SPINAL NERVE-ROOTS. 

From the number of the nerve or of the vertebra below, which 
the nerve escapes from the spinal canal, subtract one in the cervical 
region, two in the upper thoracic region, three in the lower thoracic 
region, and this will give you the level at which the nerve-roots 
arise from the spinal cord. 

The lumbar roots arise between the tenth and eleventh thoracic 
vertebrae; the sacral roots at the level of the twelfth thoracic 
vertebra. 



TABLE OF DIFFERENT KINDS OF SENSIBILITY. 



Epicritic 



Protopathic 



Temperatures between 26 

and 37 C. 
Tactile 
Localization 

Temperatures below 26 and 

above 37 C. 
Heat 
Cold 
Pain 



Deep Sensations { % j 

( Space ( Positions of 

i loints a.no 



Conscious through cutaneous 
sensory nerves. 



Conscious or unconscious 
through nerves which run 
with motor nerves. 



Stereo-gnostic 



Conscious deep sensibility. 



Weight 

Quality of / Pressllre 
surface ^ Tactile-epicritic 

f Heat 1 

Temperature r Epicritic or protopathic. 

I. Cold J 



SPINAL CORD, COWERS' TABLE 



45 



COWERS' TABLE. 

SHOWING THE APPROXIMATE LOCALISATION OF THE VARIOUS MOTOR, 

SENSORY, AND REFLEX FUNCTIONS IN THE SEGMENTS OF THE 

SPINAL CORD. 



MOTOR (Nerves) MOTOR 


SENSORY REFLEX 




Cl) 


t\ 




i 




V Small rotators of head 


Scalp 




St.'- mastoid, ( 


a ) Depressors of hyoid 


4 




2 


Upper neck 1 










muscles, J 
Upper parti 


3 ) 

> Lev. ang. scapulas 

A i i 


3^ 


Neck and upper 
part of chest 


3 


of 
Trapezius | 


1 

V Diaphragm ^ 
S\ ) fc 


4 


i Shoulder 


4 




1 Scalene 1 TS 2 


5 ) 




5 r 






VRnomboids \-~3 in 


I 


Arm, outer side 








1 Serratus I ja g 


6 ) 









Lower neck 
muscles, 


/ Flex, of elbow 1 ^ 
> 1 Supinators J 
f Ext. wrist & fingers 




Radial side, fore- 
arm and hand ; 
thumb 


7 


Scapular 


Middle part./ 


7 ) Ext. elbow 


^j 


Arm, inner side, 






of | 


> Flex, wrist & fingers 


H 


ulnar side of fore- 


8 




Trapezius 


8 ) Pronators 


f 


arm and hand ; 






I 


.D 1 > Muscles of hand 


- 


tips of fingers 


i. 






a' 


2 




2 




3 


3 




3 




4 


4 




4 






5 


S 


Front of Thorax 


5 




Lower part 
ol 


6 Intercostals 


6 


! Ensiform area 


6 


Epigastric 


Trapezius ( 


7 ' 


7 




7 




and dorsal 








8 : 




muscles 


8 


/ 










9 


9 




9 






loj Alxlominal muscles 


10 


Abdomen 
(Umbilicus loth) 


10 


Abdominal 




ii 


ii 


X Buttock, 


ii 






,3 


12 


i upper part 


12 




L umbar 
muscles 

Peronei. 
Flex, ol J 
ankle, Ext. j 
of ankle \ 


Ll 

!a ) Cremaster 
j" Flexors of hip 
3 ) Extensors of knee 
4 Abductors of hip 
) Ext. and abductors 
5 ) of hip 
s ) Flexors of knee 
f Intrinsic muscles of 
a ^ foot 


i ) Groin and Scrotum 
(front) 
/outer side 

3 1 Thigh I front 
4 1 ( inner side 
5^ Leg, inner side 
1 / Buttock, lower par 
i ( J Back of thigh 
f i Leg & ) except 
1 (. foot ) inner part 


I 

2 

3 

4 
S 

i 

2 


Cremasteric 
\Ktter-jerk 

.Gluteal 

\ Foot- 
l clonus 

> Plantar 




^ % Perineal and anal 


3 




3" 




4 j muscles 


4 J 


Perinaniin and anus 


4 




5 


) Skin from coccyx to 


5 




Co. 


,co. 


anus 


CO. 



46 THE CENTRAL NERVOUS SYSTEM 



SECTION II. 



DISSECTIONS OF THE PARTS OF THE BRAIN. 

Before proceeding with the description of the brain, 
it may be well to give seriatim, the dissections required 
to expose the several parts, so that the subsequent 
account may be the less disconnected, and therefore 
more easily understood. You can refer to them as 
required, for the pages will be placed at the head of 
each section. 

DISSECTION. i. To expose the Membranes of the Brain. Make an 
incision across the vertex of the head from ear to ear. Turn back 
the scalp to the level of the external occipital protuberance behind, 
and to the root of the nose in front. Saw through the outer table 
of the skull-cap along a line passing round the skull, about half- 
an-inch above the external occipital protuberance behind, and 
about the same distance above the supra-orbital arch in front. 
Break through the inner table with the chisel and forcibly raise the 
detached skull-cap, which you will find more or less adherent to 
the subjacent membrane, especially along the lines of the cranial 
sutures. This dissection will expose the outer surface of the dura 
mater. Branches of the meningeal arteries will be seen ramifying 
on the outer surface of the exposed membrane, between it and 
the bone. 

2. To remove the Brain. With a sharp pair of scissors cut 
through the dura mater at the same level at which you have sawn 
the bones, and reflect it upwards towards the top of the head. 
Examine as far as you can the strong process, falx major, passing 
down mesially between the cerebral hemispheres. Divide this 
process in front where it is attached to the crista galli of the 
ethmoid, and cut through the veins which enter the sinus contained 
within its upper border. Raising the falx out of the longitudinal 



DISSECTIONS OF PARTS OF THE BRAIN 47 

fissure, turn it back, but do not cut it behind. Now pass the fingers 
of the left hand beneath the fore part of the brain, and gently raise 
it from the anterior cranial fossae, taking care to detach the small, 
white, rounded bands, OLFACTORY LOBES, ist pair of cranial nerves, 
from the cribriform plate of the ethmoid. The optic nerves, -2nd pair, 
and the two INTERNAL CAROTIDS will now be seen close to the 
anterior clinoid processes, and should be divided. Piercing the 
dura mater, external to the carotids, are the round yd nerves, and 
in the free margin of the tentorium cerebelli, now exposed, are seen 
the slender $th nerves. Cut through these, and through the 
INFUNDIBULUM which passes down towards the sella turcica of 
the sphenoid. Then with the point of the knife make an incision 
through the attached margin of the tentorium on each side, just 
behind and parallel to the upper border of the petrous part of the 
temporal bone, carrying the incision as far back as necessary, but 
being careful not to injure the parts beneath. You will now see 
the following cranial nerves, which will require to be divided one 
after the other. Just below the anterior end of the tentorium will 
be found the large $th nerves ; nearer the middle line, the slender 
6th nerves ; below and external to the fjth are the jth or facial, and 
8th or auditory nerves, and the auditory artery ; immediately below 
the 8th are the gth, loth, and nth nerves. Cut the gth, or glosso- 
pharyngeal, and the loth, the vagus, but leave intact the spinal part 
of the 1 1 th nerve, the spinal accessory; lower down near the middle 
line is the 1 2th or hypoglossal nerve, consisting of two bundles, which 
pierce the dura mater by two separate openings. Next pass the 
knife as far down the spinal canal as possible, and divide the spinal 
cord, the nerve-roots attached to its sides, and the vertebral arteries 
as they wind round from the back. Snip through the vein of Galen, 
and the brain can now be easily removed from its bed, and should 
be at once placed in spirit or in a solution of formalin. Leave it 
there for a few days ; then examine it and carefully remove the pia 
mater, except at the back of the brain between the cerebrum and 
cerebellum, in order not to disturb a process of pia mater the 
velum interpositum which passes into the brain at this point. 

3. To expose the Corpus Callosum. Place the brain upon its base 
with the convex surface uppermost. Take a large sharp knife, 
moistened in spirit, and cut from the right hemisphere a horizontal 
slice about half-an-inch in thickness. This will expose an oval- 
shaped central white mass of nervous substance in the hemisphere 
the centrum ovale minus, studded here and there with small red 



48 THE CENTRAL NERVOUS SYSTEM 

spots puncta vasculosa the cut ends of the blood-vessels. 
Surrounding the white centre is the wavy grey edge, about one- 
eighth of an inch thick, the cerebral cortex before referred to. 

Remove a series of slices similar to the first, until you reach the 
level of the upper surface of the corpus callosum ; then, with one 
sweep of the knife, cut off the opposite hemisphere to this same 
level, when you will see the centrum oval majus, under which term 
is included the whole area of white matter now exposed. The 
upper surface of the corpus callosum is marked by a mesial groove, 
the rapht 1 , and by median and lateral longitudinal stria. Procure, if 
possible, a second brain, and make a mesial section of it, to enable 
you the better to examine the corpus callosum and the parts 
beneath. 

4. To expose the Lateral Ventricles. i. THE BODY. Cut through 
the corpus callosum a little on each side of and parallel to the middle 
line, and with the back of the knife raise its fibres, being careful not 
to injure the parts seen in the floor of the cavity beneath. 
Enumerated from before backwards, these parts are 

(1) The nucleus caudatus of the corpus striatum (fig. 68, page 158). 

(2) The stria terminalis or taenia semicircularis, ,, ,, 

(3) The optic thalamus, ,, 

(4) The choroid plexus, ,, ,, 

(5) The edge of the fornix, ,, 

2. CORNUA. Next trace the cavity, forwards and outwards, as 
it winds round the front of the caudate nucleus into the frontal lobe 
this is the anterior horn ; then follow it backwards into the occipital 
lobe the posterior horn ; and downwards and outwards into the 
temporal lobe the descending or lateral horn. 

In the posterior horn you will see the hippocampus minor and the 
bulb of the posterior horn (fig. 70, page 160) ; in the descending horn, 
the hippocampus major, the pes hippocampi (fig. 70, page 160), the 
leenia hippocampi, and part of the choroid plexus of the lateral 
ventricles (fig. 70, page 160), 

5. To expose the Fornix, the Septum Lucidum, and the 5th Ventricle 
(fig. 70, page 160). Make a transverse incision through the centre 
of the corpus callosum, and turn its ends backwards and forwards. 
Pass a sharp knife along the fore part of the under aspect of the 
corpus callosum, and sever its attachment to the septum lucidum. 
Lift up the anterior part of the corpus callosum, when you will 
expose the SEPTUM LUCIDUM, and the cavity enclosed between its 
two layers the 5TH VENTRICLE. Next reflect the posterior half of 



BRAIN, MEMBRANES AND VESSELS 49 

the corpus callosum, detaching it with the greatest care from the 
subjacent fornix, where the two are blended together. This will 
expose the body of the fornix. 

6. To expose the Velum Interpositum and the yd Ventricle (fig. 71, 
page 164, and fig. 72, page 166). Cut transversely through the 
middle of the fornix, and turn back the cut ends; the VELUM 
INTERPOSITUM, a delicate process of pia mater, will thus be brought 
into view. Examine this velum, and then detach it in front and 
throw it backwards so that it may be again replaced if needed. 
The 3RD VENTRICLE will be seen beneath it, extending to the base 
of the brain between the optic thalami. In front are the anterior 
commissure, the columnce fornicis or anterior pillars of the fornix, and 
the foramina interventricularia or foramina of Monro ; behind are 
the pineal gland and its peduncles; the posterior commissure, the 
corpora quadrigemina, and the aquceductus cerebri or aquceduct of 
Sylvius ; while crossing the space transversely is the middle com- 
missure or massa intermedia. 

7. To expose the Capsules. Cut horizontally through an entire 
brain or through one side only, a little below the level of the corpus 
callosum, this will give you a specimen similar to the one from 
which fig. 75, page 170 was taken. 

8. To expose the Structure of the Crura Cerebri. Slice through the 
crura at right angles to their surface; this will show you the 
arrangement of the grey and white matter. (See fig. 54, 
page 96.) 



BRAIN, MEMBRANES AND VESSELS. 

(Dissection, page 46.) 

THE term Brain, or Encephalon, includes all that part 
of the great central nervous system which is enclosed 
within the cavity of the cranium. On an average it 
weighs from 40 to 50 oz. 1 Invested by three mem- 
branes or meninges, it presents, as you will afterwards 
see, four distinct subdivisions: (i) the CEREBRUM, a 
large convoluted mass or big brain ; (2) the CERE- 
BELLUM, the delicately convoluted little brain ; (3) the 

1 Male 1360 gms., 49 to 50 oz. ; female 1250 gms., 44 oz.; children at 
seven years 1305 gms., 42 oz. 



50 THE CENTRAL NERVOUS SYSTEM 

PONS VAROLII, a white transverse band uniting the two 
halves of the cerebellum ; and (4) the MEDULLA 
OBLONGATA, or bulb, the enlarged upper end of the 
spinal cord (figs. 28 and 29, page 50 ; fig. 66, page 148). 
From a developmental point of view, the brain is 
divided into three primary parts; which, named from 
before backwards, are the Prosencephalon, fore-brain ; 
the Mesencephalon, mid-brain ; the Rhombencephalon, 
lozenge-shaped brain. By subsequent divisions we get 
five segments : the Telencephalon, end-brain ; Dien- 
cephalon, inter- brain; Mesencephalon, mid-brain; (the 
Isthmus Rhombencephali, lozenge - shaped brain) ; 
Metencephalon, after - brain ; Myelencephalon, the 
marrow-brain (see Development, page 232). 

We shall describe (i) the membranes and vessels of 
the brain, (2) the several parts of the brain, and (3) the 
cranial nerves. 

CHAPTER I. 

MEMBRANES OF THE BRAIN. 

(Plate VII. Page 58; Plate VIII. Page 59). 

To examine the first of these membranes the cranial 
dura mater replace, as far as you can, the falx major 
and the tentorium cerebelli, and fasten them in their 
places by a few stitches. It will, however, be far more 
satisfactory for you if you can obtain a specimen 
specially prepared to show the arrangement of the 
dura mater. 

1. THE DURA MATER. 

The Cranial Dura Mater is a dense, white, fibrous 
membrane, rough externally, but smooth and polished 
within, where it is lined by a layer of epithelial cells 
similar to that which lines the spinal dura mater. 



Pedunculi cerebn. 
Brachia pontis 

Pans Varolii, 



Cisttrna pontis 
Subarachnoid spar.r 




Velum 
interpositum 



Subdural 
space. 

Cistema basilaris 



Cerebellum. 



Foramen 
Magendie. 

Cistema 
Magna. 



BRAIN, MEMBRANES, DURA MATER 51 

Much thicker than the spinal dura mater, it is 
composed of two layers, an inner and an outer, though 
in the greater part of their extent these are blended 
and are not distinct from each other. The inner layer 
sends processes or partitions between certain parts of 
the brain, and the outer adheres to and forms the 
endosteum of the inner table of the cranium. In two 
places especially is this attachment of the outer layer 
well marked, firstly along the lines of the cranial 
sutures, and secondly at the base of the cranium. 
This latter fact accounts for the rare occurrence of 
accumulations of pus or blood at the base of the brain 
between the dura mater and the bone. The dura 
mater, moreover, sends a tubular process round each 
of the several cranial nerves as they leave the skull 
through their various foramina; part of this tubular 
process forms a sheath to the nerve, part of it becomes 
attached to the pericranium. Similar processes also 
extend into the orbital cavities, and there blend with 
the periosteum. At the lower margin of the foramen 
magnum the dura mater is closely adherent to the 
bones, and becomes continuous with the spinal dura 
mater. Although, in the greater part of their extent, 
the two layers of the dura mater are, as we have said, 
blended together, along certain lines they separate from 
each other, leaving between them variously shaped 
channels, called VENOUS SINUSES, for the passage of 
the blood from the brain into the venous system. 

Of the partitions given off from the inner layer, 
two the FALX CEREBRI and the FALX CEREBELLI 
are vertical ; the third, the TENTORIUM CEREBELLI, is 
nearly horizontal, sloping downwards and backwards 
between the cerebrum and the cerebellum. 



52 THE CENTRAL NERVOUS SYSTEM 

1. The Falx Cerebri so called from its sickle- 
shaped form (fig. 32, page 58) is the vertical mesial 
process of dura mater which is lodged in the great 
longitudinal fissure of the cerebrum, and separates 
the inner surfaces of the cerebral hemispheres from 
each other. In front it is pointed, and is attached 
to the apex and to the posterior margin of the crista 
galli. Behind it widens out, forms the base of the 
sickle, and becomes continuous along the middle line, 
with the upper surface of the tentorium cerebelli. 
Its upper convex margin contains the superior 
longitudinal sinus, and adheres to the ridges seen on 
each side of the median depression on the deep aspect 
of the vault of the skull. The lower margin contains 
the inferior longitudinal sinus. It is concave and free 
and is in contact behind with the upper surface of the 
great cerebral commissure, called the corpus callosum, 
though it is some distance from it in front. 

2. The Falx Cerebelli (fig. 3 2 > page 58) is the 
small, median, vertical, triangular partition, attached 
behind by its convex border to the internal occipital 
crest, and above, at its widest part, to the mid-line 
of the under surface of the tentorium cerebelli. Its 
anterior, free, concave margin projects forward, and 
fits into the notch between the two halves of the 
cerebellum. Its posterior attached margin contains 
the occipital sinus. This sinus is single above, but 
bifid below. 

3. The Tentorium Cerebelli (fig. 32, page 58), 
supporting the posterior part of the cerebrum, slopes 
forwards and upwards, somewhat horizontally, as an 
arched, tent-like partition between the big and the 
little brain. The posterior convex margin is attached 



BRAIN, MEMBRANES, DURA MATER 53 

behind to the transverse ridges on each side of the 
grooves on the inner aspects of the occipital and 
parietal bones. Further forwards it is fixed to the 
upper margins of the petrous part of the temporal 
bones. It ends in front at the posterior clinoid pro- 
cesses. This margin contains the lateral sinuses 
behind, and the superior petrosal sinuses in front. 
The anterior, concave, V-shaped margin is free in the 
greater part of its extent, but, in front, it is attached 
on each side by two narrow slips the ends of the 
V to the anterior clinoid processes. Between this 
free margin and the dorsum sellae of the sphenoid is 
an oval opening the tentorial notch for the passage 
of the crura cerebri, of the superior peduncles of the 
cerebellum, and of the posterior cerebral arteries. 
Along the middle line of the upper surface of the 
tentorium runs the straight sinus, which receives the 
vein of Galen vena cerebri magna from the interior 
of the cerebrum (fig. 32, page 58). 

The MINUTE STRUCTURE of the dura mater of the 
brain is similar to that of the spinal cord. It consists 
of layers of fibrous tissue. The larger arteries lie 
near the outer surface of the membrane, whereas the 
veins are embedded in its midst or lie between its 
layers. There are few capillaries in its substance, 
but on its inner aspect is a rich network of vessels 
covered by epithelial cells and surrounded by peri- 
vascular spaces which, by means of stomata, com- 
municate with the sub-dural space (Robertson). 

The cranial dura mater receives its nerve-supply 
from the 4th, the 5th, and the loth cranial nerves, and 
from the autonomic system. 

Pacchionian Bodies or arachnoid granulations, (fig. 



54 THE CENTRAL NERVOUS SYSTEM 

34, page 58) are small, white elevations of lymphoid 
tissue which indent the inner surface of the vertex of 
the skull. They mostly occur along each side of the 
middle line, near the superior longitudinal sinus. 
Others are found near the lateral, cavernous, petrosal, 
and straight sinuses. They are said to be outgrowths 
of the villi, which normally exist in the arachnoid ; their 
exact nature and use is, however, unknown. Some 
hold that they are mere excretions, others that they 
are communications between the sub-arachnoid space 
and the venous sinuses of the dura mater, and others 
that they are ligaments which fix the pia mater to 
the dura mater and help to suspend the brain. 

2. THE PIA MATER. 
(Fig. 29, Page 50, and Fig. 30, Page 58). 

The Pia Mater of the brain, like that of the spinal 
cord, is an extremely fine vascular membrane, com- 
posed of a plexus of capillary blood-vessels, held 
together by delicate connective tissue (fig. 30, page 
58). It is practically one layer with the arachnoid. 
Covering the surface of the brain, it dips into the 
various fissures between the convolutions of the 
cerebrum, but into the larger fissures only, in the case of 
the cerebellum. From its inner surface numberless 
blood-vessels emerge for the nourishment of the 
substance of the brain. Besides the septa between 
the convolutions, the pia mater also sends into the 
cerebrum through a large fissure, called the great 
transverse fissure, a special prolongation covered with 
epithelium the velum interpositum, the margins of 
which are wrinkled and folded forming a vascular fringe, 
called the choroid plexus or tela choroidea superior. 



BRAIN, MEMBRANES, PIA MATER, ARACHNOID 55 

A similar vascular process of the pia mater, known as 
the tela choroidea inferior, or choroid plexus of the 
4th ventricle, lies in the roof of that cavity (see pages 
124 and 164). 

In STRUCTURE the pia mater of the brain corre- 
sponds to the inner of the two layers of the pia- 
arachnoid described on the following page. It 
receives its nerve-supply from the 3rd, 5th, 6th, 
7th, and 8th cranial nerves, as well as from the 
sympathetic. 

3. THE ARACHNOID. 

The Arachnoid is a very delicate, smooth, glistening, 
transparent, colourless membrane, situated between the 
dura mater and the pia mater (fig. 30, page 58). It has 
neither blood vessels nor nerves. Its outer surface is 
covered by minute reddish-grey villi (see Pacchionian 
bodies, page 53). Formed of a single layer, it is, on the 
one hand, separated from the dura mater by the sub- 
dural space, and, on the other, envelops the brain, but 
does not pass into the fissures between the convolutions, 
though it dips into the superior longitudinal fissure, and 
into the fissure between the cerebrum and the cerebellum. 
It is closely connected with the pia mater beneath by 
the sub-arachnoid trabeculae, which are far more numerous 
than those in the spinal cord. 

MINUTE STRUCTURE. The arachnoid is not, strictly 
speaking, a distinct membrane from the pia mater, and 
the two are often described together under the name pia- 
arachnoid. This consists of two layers of epithelium 
a superficial and a deep the latter being in contact 
with the brain. The two layers are united by numberless 
delicate threads of fibrous tissue, clothed with epithelial 
cells, and called sub-arachnoid trabeculae. 



56 THE CENTRAL NERVOUS SYSTEM 

Sub dural and Sub arachnoid Spaces (fig. 29, page 
50). The space between the dura mater and the arach- 
noid is called the sub-dural space, and is lined by 
epithelial cells. The space between the arachnoid and 
pia mater is the sub-arachnoid space, and is crossed by 
the sub-arachnoid trabeculae. It contains cerebro-spinal 
fluid. Both its inner and outer walls are lined by 
epithelial cells, which also cover the surfaces of the 
trabeculae. At certain spots, especially at the base of 
the brain, the pia mater and the arachnoid are more 
widely separated from each other, forming specially 
named parts of the SUB-ARACHNOID SPACE. These parts 
are most distinct in the following situations : (i) above, 
at the great longitudinal fissure ; (2) at the base of the 
brain, forming the cisterna basilaris; (3) in front of the 
pons, forming the cisterna pontis ; and (4) behind, be- 
tween the cerebellum and the medulla oblongata, forming 
the cisterna magna. 

Cerebro-spinal Fluid. Most of this fluid is contained 
in the meshes of the sub-arachnoid trabeculae, though 
a small quantity is found in the sub-dural space. It 
is secreted by the choroid plexus of the velum inter- 
positum. Through an opening \htforamen of Majendie 
in the roof of the 4th ventricle (fig. 29, page 50), and 
through two similar lateral openings in the ventricular 
roof between the medulla and cerebellum, the cerebro- 
spinal fluid of the sub-arachnoid space is continuous 
with the fluid in the central canal of the spinal cord 
and in the cavities or ventricles inside the brain. Corre- 
sponding communications also exist at the inferior 
horns of the lateral ventricles. The cerebro-spinal 
fluid is not merely intended to fill the sub-arachnoid 
space, but to help to protect the nerve-centres from 



BRAIN, MEMBRANES, VENOUS SINUSES 57 

sudden shocks, acting, in fact, as a water-bed on which 
the brain rests (Hilton). Being of the nature of lymph, 
it is probable that the cerebro-spinal fluid may also 
subserve the nutrition of the brain. 



4. VENOUS SINUSES. 
(Fig, 31, Plate VII. Page 58; Figs. 32. etc., Plate VIII. Page 58). 

The sinuses of the dura mater are formed by the 
separation of its two layers. They are lined by epithelial 
cells continuous with the cells lining the interior of the 
veins. These sinuses are seventeen in number six 
paired and five single. The single sinuses are the 
superior and the inferior longitudinal, the straight, the 
circular, and the transverse or basilar. The paired set 
includes the two lateral, the two superior and the two 
inferior petrosal, the two cavernous, the two occipital, 
and the two spheno-parietal. 

i. The Superior Longitudinal Sinus S. Sagittalis 
Superior (figs. 32 and 33, page 58) begins in front at 
the foramen caecum as a small vein, which often com- 
municates with the veins of the nose. Arching upwards 
and backwards in the convex margin of the falx cerebri, 
on the deep aspect of the middle line of the calvaria, 
it reaches the internal occipital protuberance, where it 
is joined by several other sinuses at the triangular 
dilatation, called the torcular Herophili, 1 or the meeting 
of the sinuses. Cut open the sinus in its entire length 
and you will see that it forms a gutter which increases 
in size as it passes backwards, and which is wider above 
than below, being triangular in section. Its cavity is 

1 As Holden points out, the term torcular (a wine-press) is a 
mistranslation of the original word, <r*Xi)'r a canal or gutter. 



58 THE CENTRAL NERVOUS SYSTEM 

crossed by many slender bands chordae Willisii. 
Numerous veins, from the substance of the brain, pour 
their blood into this sinus. They run mostly from 
behind forwards, that is, in the reverse direction to the 
blood current within the sinus. They pierce the wall 
of the sinus by slit-like openings, which act as valves, 
and thus prevent regurgitation of the blood. Before 
entering the sinus they often pass through small spaces, 
called the para-sinoidal spaces, which lie on each side 
of the superior longitudinal sinus (fig. 34, page 58). 
Other smaller veins enter this sinus from the diploe 
of the surrounding bones, and it receives a large emissary 
vein through the parietal foramen. 

2. The Inferior Longitudinal Sinus 5. Sagittalis 
Inferior (figs. 32, 33, page 58) is really a small vein 
contained in the free concave border of the falx major. 
It commences in front by minute venous radicles within 
the substance of the falx major, and it ends behind in 
the straight sinus. 

3. The Lateral Sinuses S. Transversi(ftg. 31, 
page 58) are two in number, right and left, the right 
being usually the larger. Through them most of the 
venous blood from the brain reaches the internal jugular 
veins. They commence at the internal occipital pro- 
tuberance, and running outwards in the attached margin 
of the tentorium cerebelli, in the grooves on the inner 
surface of the occipital and parietal bones, finally turn 
downwards and forwards in the sigmoid groove on the 
mastoid part of the temporal bone and on the jugular 
process of the occipital bone, to end in the bulb of 
the internal jugular veins. This part of the sinus is 
often called the sigmoid portion of the lateral sinus. 
Blood enters these sinuses from the superior and inferior 



FIG. 30 



Middle meningeal. 



Dura mater. . 




PLATE VII. 



Pacchionian bodiex. 



'ia mater. 



Cerebral veins. 



-Arachnoid. 



FIG. 31. 



Anterior 
meningeal artery 



S. circularis. 



Middle 
meningeal artery. 



S. occipitalis. 



Ophthalmic veins. 



S. cavemosvs. 




\- S'. transvers-us. 



', petrosus super 
S. petrosus infer. 



Venous Sinuses. 



Cummin? 



PLATE VIII. 



FIG. 32. 



Falx cerebri. 




S. petrosal inf. 



S. petrosal sup. 



Sinus sagittate 

super. 



Sinus rectus 

Sinus lateralis. 
Falx cerebelli. 

S. occipitali*. 



. 33. 




S. Sa.gitta.lia p, G . 34 

sup. 

Pacchumian 

Subdural Parasimndal 

space. 



Sagittalis 

sup. 
ra mater. 

Arachnoid. 




Pia mater. 



S. petrosal inf. 



Int. jug v. 



S. occipitalis. 



Sub. arachnoid* 
space. 



Sinuses. 



BRAIN, MEMBRANES, VENOUS SINUSES 59 

petrosal sinuses, from the inferior cerebral and cerebellar 
veins, and from the diploe of the bones. By means of 
emissary veins, which pass through the mastoid and 
anterior condyloid foramina, they communicate with 
the veins of the scalp. 

4. The Straight Sinus 5. Rectus(hg. 32, page 58) 
lies in the middle line of the upper surface of the 
tentorium cerebelli, where the falx major is attached. 
Behind, it ends at the meeting of the sinuses, while in 
front it receives the inferior longitudinal sinus and the 
vena cerebri magna or vein of Galen, the latter bringing 
blood from the third and the lateral ventricles of the 
brain. Some cerebral and cerebellar veins also open 
into this sinus. 

5. The Cavernous Sinuses (fig. 31, page 58), so 
called from the spongy arrangement of the connective 
tissue in their interior, are placed in the grooves on each 
side of the body of the sphenoid. They are oval in 
vertical transverse section, and contain, in their thickened 
outer wall, the third, the fourth, and the ophthalmic and 
superior maxillary divisions of the fifth nerves ; while 
internally, and separated from the blood of the sinus 
by a thin lining membrane, is the internal carotid artery, 
with the sixth nerve on its outer side. These sinuses 
communicate with the circular sinus, and with the 
superior and inferior petrosal sinuses. Small cerebral 
veins and the veins from the orbits (fig. 31, page 58), 
and from the pterygoid plexus of veins, open into these 
sinuses. 

6. The Circular Sinus (fig. 31, page 58) is really 
a plexus of veins which completely surrounds the 
pituitary body in the sella turcica. At each side it 
communicates with the cavernous sinuses. 



60 THE CENTRAL NERVOUS SYSTEM 

7. The Petrosal Sinuses (fig. 31, page 58) are two 
on each side the superior and the inferior. The 
Superior Petrosal Sinus lies along the upper border of 
the petrous part of the temporal bone, and connects 
the cavernous sinus with the lateral sinus at its highest 
point. The Inferior Petrosal Sinus runs in the groove 
between the occipital bone and the petrous part of the 
temporal bone. It unites the cavernous sinus to the 
lateral sinus after the latter has passed out of the skull 
to become the internal jugular vein. Cerebral, cerebellar, 
tympanic, and auditory veins pour their blood into one 
or other of these sinuses. 

8. The Transverse or Basilar Sinus (fig. 31, page 
58), sometimes double, is placed across the basilar 
process of the occipital bone, and connects together 
the inferior petrosal sinuses. It is in reality a plexus 
of veins and not a mere sinus. It communicates below 
with the anterior spinal veins. 

9. The Occipital Sinuses (fig. 31, page 58) com- 
mence near the foramen magnum as two small channels 
which run upwards in the attached margin of the falx 
cerebelli, and then join above to form a single sinus 
which opens into the torcular Herophili. 

10. The Spheno-parietal Sinuses are two small 
venous channels which are found along the posterior 
margin of the lesser wing of the sphenoid. They open 
into the cavernous sinus of the corresponding side. 

Emissary Veins are small vessels which pass through 
foramina in the skull, and unite the veins of the scalp 
with the cranial sinuses. " If it were not for these veins 
injuries to the scalp would lose half their significance " 
(Treves). 

The Meningeal Arteries, which supply the dura mater 



BRAIN VESSELS, ARTERIES 61 

with blood, ramify in branching grooves on the inner 
surface of the cranium, between it and the outer surface 
of the dura mater (fig. 31, page 58). From the cranial 
fossae in which they ramify, they are called the anterior, 
the middle, and the posterior meningeal arteries, and 
they arise from the ethmoidal, ascending pharyngeal, 
internal maxillary, occipital, and vertebral arteries. The 
larger veins are superficial to the arteries and lie next 
the bones. For the description of these vessels see your 
dissecting manual. We shall now pass on to examine 
the vessels of the brain. 

CHAPTER II. 
VESSELS OF THE BEAIN. 

(Figs. 35 and 38, Plate IX. Page 62. and Fig. 39, Plate X. Page 64). 

DISSECTION. Remove the pia mater with great care, and in doing 
so, at the under surface of the brain, dissect out the vessels and 
the cranial nerves. 

Note. Those who have no previous knowledge of the brain might 
do well to read Chapter III. first, page 68, and then turn to the 
perusal of this chapter. 

I. Arteries. The arteries of the brain are derived 
from two sources, from the two internal carotids and 
from the two vertebrals. 

THE INTERNAL CAROTID ARTERIES, when they 
reach the anterior clinoid processes, give off the 
ophthalmic branches, and then divide into anterior and 
middle cerebral, and posterior communicating. 

i. The ANTERIOR CEREBRAL ARTERIES run forwards 
to the fore part of the great longitudinal fissure, and 
curving round the anterior end of the corpus callosum, 
pass backwards on its upper surface, under the name 



62 THE CENTRAL NERVOUS SYSTEM 

of the arteries of the corpus callosum. At their com- 
mencement they are joined by a short transverse 
branch the anterior communicating; while behind they 
anastomose by small branches with the posterior 
cerebral arteries. 

The anterior cerebral arteries give oft' two sets of 
branches (a) a cortical set, and (b] a basal set. 

(a) The cortical set, after ramifying and anastomosing 
within the pia mater, perforate the convex aspect of 
the brain at right angles to the surface, and supply the 

fore and upper parts of the inner surface of the hemi- 
spheres as far back as the parieto-occipital fissure. 
They also supply the inner part of the outer and lower 
aspects of the frontal lobes (figs. 39, etc., page 64). 

(b) The basal set enter the anterior perforated space 
and are distributed to the front part of the corpus 
callosum and to the interior of the cerebrum, viz., to 
part of the caudate nucleus and of the internal capsule 
(see Table, page 67). 

2. The MIDDLE CEREBRAL Or SYLVIAN ARTERIES 
are the largest branches of the internal carotid. They 
run upwards and outwards in the fissure of Sylvius till 
they reach the island of Reil, when they ramify in the 
pia mater, and anastomose with the anterior and 
posterior cerebral arteries (fig. 38, and page 62). 

Like the anterior cerebrals, they give off cortical 
and basal branches. 

The cortical branches, four in number, are distributed 
to the outer surface of the parietal lobe and to the 
adjacent parts of the frontal and temporal lobes (figs. 
38, and 39 etc., page 62, and page 64). 

The basal branches are furnished, through the anterior 
perforated space, to the corpus callosum and to part 



FIG. 35. 



Fornix. 



PLATE IX. 



Corpus callosum. 



Posterior cerebral. 



Superior 

cerebeilar. 



Anterior 
communicating. 

Internal 
carotid. 
Posterior 
communicatin^ 

Superior 
cerebeilar. - 



Anterior^ 
Middle > cerebral. 
Posterior^ 



nterior cerebral. 
Anterior chotoidal 




Posterior 
communicating. 

Superior cerebeilar. 
Transverse branch. 



Posterior 
inferior cerebeilar \ 



Anterior spinal. 



LettticiUar 
striate 
'osterior cerebral. 



nterior inferior 
cerebeilar. 

Vertebral. 



Arteries of the Brain. 



BRAIN VESSELS, ARTERIES 63 

of the internal capsule and of the corpus striatum. 
They are all terminal arteries, by which we mean that 
they do not anastomose with each other. They are 
sometimes called the ganglionic system of arteries. 
They will be again referred to in describing the central 
grey matter of the hemispheres (page 182). The middle 
cerebral artery is the one chiefly concerned in cerebral 
haemorrhage. 

3. The ANTERIOR CHOROIDAL ARTERIES, one or 
two in number, are either branches of the internal 
carotids or of the middle cerebrals. Entering the fissure 
between the temporal lobe and the crus cerebri (figs. 
35 and 38, page 62), they reach the descending cornu 
of the lateral ventricle, and there form the vascular 
fringe called the choroid plexus. They also supply the 
uncinate gyrus of the temporal lobe, and part of the 
posterior limb of the internal capsule. 

4. The POSTERIOR COMMUNICATING ARTERIES run 
backwards and join the posterior cerebral arteries 
(branches of the basilar artery), and thus is established 
a free anastomosis between the carotids and the 
vertebrals (see Table, page 67). 

The VERTEBRAL ARTERIES branches of the sub- 
clavian enter the foramen magnum by perforating, first 
the posterior occipito-atlantal ligament, and then the 
dura mater. They curve round to the anterior surface 
of the medulla between the I2th cranial nerve and the 
anterior roots of the 1st cervical nerve. At the lower 
border of the pons they unite to form a single trunk 
the basilar artery which runs in the groove on the 
front of the pons, till it reaches its upper margin, when 
it divides into the two posterior cerebral arteries (fig. 
38, page 62). 



64 THE CENTRAL NERVOUS SYSTEM 

1. BRANCHES OF THE VERTEBRAL ARTERIES. Only 
one branch, the posterior inferior cerebellar, which may, 
however, sometimes be a branch of the basilar, is given 
off by the vertebral artery to the brain. It chiefly 
supplies the under surface of the cerebellum. 

2. BRANCHES OF THE BASILAR (fig. 38, page 62) : 

(1) Transverse branches, three or four in number, 
run transversely outwards on the pons and supply it. 
One branch the internal auditory enters the internal 
auditory meatus. 

(2) The anterior inferior cerebellar arteries are 
distributed to the anterior part of the lower surface of 
the cerebellum, and anastomose with the other cere- 
bellar arteries. 

(3) The superior cerebellar arteries, given off near 
the termination of the basilar, supply the upper surface 
of cerebellum, and send branches to the valve of 
Vieussens, to the pineal gland, and to the velum 
interpositum. 

(4) The posterior cerebral arteries the terminal 
branches of the basilar curve outwards and backwards, 
round the outer side of the crura cerebri, to the under 
surface of the posterior cerebral lobes, supplying them 
and anastomosing with the anterior and the middle 
cerebral arteries. They send basal branches to the 
posterior perforated spot and to the vellum interpositum 
(posterior choroidal), and give off three cortical branches 
(fig. 38, page 62), which supply the occipital lobe, part 
of the quadrate lobe, and the mesial and contiguous 
parts of the outer surface of the temporal lobe (figs. 
39 and 42, page 64). 

Circle of Willis. This important arterial inosculation 
takes place at the base of the brain between the 



PLATE X. 



FIG. 39 



Anterior cerebral 

Eye 
Movements 

Motor centres 
for 

a. Head and neck. 

b. Upper limb. Hearing 
r. Trunk. 

I Lower limb. 

FlG. 40 




Cutaneous \ 
muscular \Sensatum 
joint 



Middle cerebral. 
Word seeing 

Sight 



Posterior cerebral 




FIG. 42 
Anterior cerebral 

, ' * Motoi 



Middle Cerebral 



r>" Sensation "X 
Cc - -V 
/ . 




Humi-centn- 

/</ sight 

~wr crreliial 



Vascular Areas of Brain 



BRAIN, MEMBRANES AND VESSELS 65 

internal carotids and the vertebrals. In front the circle 
is formed by the anterior communicating artery which 
joins together the two anterior cerebral arteries ; behind 
by the two posterior cerebral arteries, branches of the 
basilar, and on each side by the internal carotids, the 
anterior cerebrals, and the posterior communicating 
(figs. 36, 37, page 62). 

CIRCLE OF WILLIS. 

In front : 
Anterior Communicating. 

On each Side : 

Left side. Right side. 

Anterior Cerebral. Anterior Cerebral. 

Internal Carotid Internal Carotid. 

Posterior Communicating. Posterior Communicating. 

Behind : 

The Two Posterior Cerebrals, 
branches of the Basilar. 

2. Veins. The veins of the brain do not accompany 
the arteries, but open into the various sinuses in the 
dura mater. They have no valves. 

In the cerebrum we have two sets of veins the one 
superficial, on the surface of the brain, the other deep. 
Of the superficial set, those above open into the superior 
longitudinal sinus ; those on the lateral and under aspect 
of the brain open into the lateral, the cavernous, and the 
superior petrosal sinuses. The deep set of veins, gather- 
ing the blood from the interior of the brain, enters the 
vein of Galen, and thus pours its blood into the straight 
sinus. In the cerebellum the veins on the upper surface 
enter the vein of Galen and the straight sinus ; those on 
the under surface end in the occipital and lateral sinuses. 

Special Characters of the Cerebral Circulation 
are 

i. The free anastomosis at the circle of Willis, 



66 THE CENTRAL NERVOUS SYSTEM 

which provides a ready supply of blood from other 
vessels in case of the sudden blocking of any of the 
more direct channels. 

2. The tortuous course through bony canals of 
the arteries as they enter the skull, thus mitigating 
the force of the heart's beat. 

3. Their ramifications in the pia mater before 
entering the substance of the brain. 

4. The thinness of the arterial walls, and the 
smallness of the capillaries. 

5. Except at the circle of Willis, and at their 
terminations by capillary vessels, there is little 
communication between the branches of the cerebral 
arteries, so that if any artery be obstructed, the 
nutrition of the area to which it is supplied becomes 
impaired. 

6. The existence of venous sinuses which are 
without valves, and which do not run with the 
arteries the larger arteries, in fact, having no 
companion veins. 

7. The venous and arterial currents on the surface 
of the brain run in the same direction, i.e, from before 
backwards. 

The figs., plate X. page 64, will give you an idea 
of the distribution of the chief arterial branches to the 
cerebral cortex, and on page 67 you will find a useful 
table for reference. 

3. Lymphatics. In the brain there are no lymphatics 
properly so called ; they are represented by spaces 
either round the nerve-cells pericellular spaces ; or 
round the blood-vessels perivascular spaces. They 
leave the brain with the blood-vessels, and end in the 
lymphatics in the neck. 



BRAIN, TABLE OF ARTERIES 



67 



Cortical set 

to 
Convolutions. 



TABLE OF THE DISTRIBUTION OF CEREBRAL ARTERIES 
FOR REFERENCE. 

Superior frontal. 

Anterior two-third of middle frontal. 

Upper end of ascending frontal. 

Inner surface of frontal lobe (marginal 

convolution). 
Mesial surface (quadrate lobe) and 

inner part of external surface of 

parietal lobe. 
Gyrus fornicatus. 
Olfactory bulb. 
Orbital surface of frontal lobe, internal 

to olfactory groove. 
Fore part of the corpus callosum. 
Septum lucidum. 

Anterior part of the caudate nucleus. 
Lower half of anterior limb of internal 

capsule. 
Inferior frontal. 
Middle frontal. 

Great part of ascending frontal. 
Orbital surface of frontal lobe outside 

olfactory groove. 

Outer surface of the parietal lobe. 
Superior and middle temporal. 
Insula. 
Corpus striatum except head of caudate 

nucleus. Optic thalamus. Upper half 

.of anterior limb of internal capsule. 
Posterior limb of internal capsule. 
The occipital lobe. 
Under or mesial aspect of temporal 

lobe except its anterior pole. 
The cuneate lobe, the posterior part of 

quadrate lobe, and part of the outer 

aspect of the parietal lobe. 
Caudate nucleus (lateral choroidal). 
Posterior limb of internal capsule 

(slightly). Optic thalamus. 
Velum interpositum and choroid plexus 
of lateral ventricle. 



Basal set 

to 
Other parts. 



Cortical set 

to 
Convolutions. 



Basal Set 

to 
Other parts. 

Cortical Set 

to 
Convolutions. 



Basal Set 

to 
Others parts 



68 



THE CENTRAL NERVOUS SYSTEM 



Anterior. 



Posterior. 



optic 



posterior limb of internal 
Uncinate gyrus. 



To anterior perforated spot. 

Crura cerebri. 

Anterior and inner part of 

thalamus. 
Posterior limb of internal capsule. 

f Choroid plexus of lateral ventricle and 
Anterior choroidal (from 

part Of r.r.ctet-1 

internal carotid). 

I capsule. 

f Optic chiasma. "\ 

- Infundibulum % v Interpeduncular space. 

Corpora mammillaria. J 

Fore part of cerebellum. 

Superior medullary velum. 

Superior peduncle of cerebellum. 

Upper surface of cerebellum. 

Choroid plexus of 4th ventricle. 

Under surface and back part of upper 

surface of cerebellum. 
Inferior corpora quadrigemina. 
Posterior perforated spot. 
Medulla. 
Pons. 
Anterior aspect of cerebellum (anterior 

inferior cerebellar). 
Cerebellum. 
Medulla. 
Pons. 



Circle of Willis, 



Anterior. 



Superior. 



Basilar. 



Vertebral. 



Inferior. 



CHAPTER III. 

BKAIN AND ITS SUBDIVISIONS. 

(Figs. 28, 29, Page 50.) 

GENERAL OUTLINE OF THE BRAIN. On placing the 
brain before you, you will see, that it is an oval- 
shaped mass of nervous substance, that has not inaptly 
been likened to the kernel of a walnut ; for " one 
cannot but be forcibly struck with the resemblance 



BRAIN, SUBDIVISIONS 69 

between the human head and a walnut. There is, 
first, the pericranium and the skin, then the bone and 
the shell ; within, the dura mater and a thick 
membrane lining the shell of the fruit ; then the pia 
mater and the delicate membrane covering the kernel, 
which is again made up of convolutions into two 
masses joined together by a commissure or corpus 
callosum"(Wilks). 

Viewed from above, the surface of the brain is seen 
to be arched and convex, and presents many tortuous 
folds or convolutions of nerve-substance, with inter- 
vening fissures or furrows, the whole giving to the 
exterior of the organ a most characteristic appearance. 
Along the middle line of this aspect of the brain runs 
a deep longitudinal cleft, which, when the brain is 
in situ, lodges the falx cerebri and divides the mass 
into two similar halves. This cleft is the great 
longitudinal fissure and the two symmetrical halves 
are called the CEREBRAL HEMISPHERES. They together 
form the first great division of the brain the 
CEREBRUM which is united to the rest of the brain 
and to the spinal cord by a mass of nerve-substance, 
known as the CEREBRAL PEDUNCLES orCRURA CEREBRI. 
On separating the walls of this median longitudinal 
fissure you will find that, in front and behind, the 
cleft extends right through to the base of the 
cerebrum, but, that in the middle of its extent, it is 
interrupted below by a transverse band of nerve-fibres, 
the CORPUS CALLOSUM, or great commissure of the 
brain. 

The under surface or BASE of the cerebrum is, in the 
greater part of its extent, convoluted like the upper 
surface, and is very irregular, for it fits into the 



70 THE CENTRAL NERVOUS SYSTEM 

corresponding fossae at the base of the skull. On 
this aspect you will recognise the other subdivisions 
of the brain (figs. 28, 29, page 50 ; fig. 66, page 148), 
viz. (i) the CFREBELLUM or little brain, lying behind 
and below the posterior part of the cerebral hemi- 
pheres ; (2) the PONS VAROLII, which, when viewed 
from the front, appears as a broad, white band about an 
inch deep crossing transversely between the two halves of 
the cerebellum ; (3) the MEDULLA OBLONGATA or bulb, 
placed between the pons above and in front, the 
cerebellum behind, and the spinal marrow below. 

The subdivisions of the brain, from a developmental 
point of view, are given on page 238. 

We shall describe (i) the MEDULLA, (2) the PONS, 
(3) the CEREBELLUM, (4) the CEREBRUM, and (5) the 
CEREBRAL PEDUNCLES. 

I. MEDULLA OBLONGATA. 
(Figs. 43 to 46, Plate XI. Page 72.) 

DISSECTION If you have only one specimen of the brain to 
work upon it will be best to pass on at once to the study of the 
cerebrum (page 126) and afterwards to return to the medulla. If 
you have more than one, then cut transversely through the crura 
cerebri, and begin the examination of the medulla. 

The Medulla Oblongata Myelencephalon marrow- 
brain, hindmost-brain is the most complicated portion 
of the central nervous system. As you already know, 
it is the expanded upper end of the spinal cord, and, 
like it, is composed of grey and white matter. It has 
an anterior, a posterior and two lateral aspects, and 
it is mapped out by fissures, similar to those of the 
spinal cord, into six columns, two anterior, two posterior 



BRAIN, MEDULLA OBLONGATA 71 

and two lateral. The anterior surface rests upon 
the basilar process of the occipital bone ; the posterior 
is hidden by the cerebellum. In general outline it 
is more or less conical, with its long axis nearly 
vertical, its base being directed upwards and forwards 
towards the Pons Varolii, its apex downwards and 
backwards, and continuous with the spinal marrow 
at the lower border of the foramen magnum. In 
length, the medulla measures about one and a quarter 
inches ; in breadth, at its widest part, about one inch ; 
in thickness about half-an-inch. Its ventral or anterior 
aspsct is convex, and is limited above by the lower 
border of the pons ; below by what is known as the 
decussation of the pyramids several bands of nerve- 
fibres which, on close examination, you will see 
crossing, at the bottom of the anterior median fissure, 
from one side of the medulla to the other side of 
the cord. Behind, that is, on its dorsal aspect, the 
medulla, in its lower half, is convex sideways, and 
resembles the spinal cord, but, in its upper half, it 
expands laterally and becomes flattened from before 
backwards, forming the lower part of the rhomboidal 
depresssion called the floor of the 4th ventricle (fig. 44 
page 72). On this aspect, the upper boundary ot 
the medulla is indicated by several transverse lines 
the stria medullares or acusticce which run across the 
widest part of the rhomboid depression (fig. 44, page 
72) ; the lower boundary is purely artificial, corres- 
ponding with the lower margin of the foramen 
magnum. Each lateral aspect of the medulla supports 
an oval eminence, the olivary body, which, in the lower 
part of its extent, as well as the surface of the medulla 
just below it, is marked by several transverse streaks, 



72 THE CENTRAL NERVOUS SYSTEM 

the external arciform fibres (fig. 46, page 72), the 
significance of which you will not, at present, understand. 
We shall now examine (i) the surface of the 
medulla, then (2) the arrangements of its grey and of 
its white matter. 



1. FISSURES OF THE MEDULLA. 

The medulla, like the spinal cord, is a symmetrical 
organ, being divided by superficial median longitudinal 
clefts anterior and posterior into two similar lateral 
segments, which are again subdivided into anterior, 
posterior, and lateral areas by the continuation up- 
wards, though not in a direct line, of the place of 
origin of the anterior and posterior spinal nerve-roots 
(fig. 46, page 72). 

1. The ANTERIOR MEDIAN FISSURE of the medulla 
is a direct continuation upwards of the anterior median 
fissure of the spinal cord. Above, at the lower 
margin of the pons, it ends in a slight recess, need- 
lessly named the foramen caecum. Below, at the 
lower limit of the medulla, it is interrupted by inter- 
lacing bands of nerve-fibres, already referred to as the 
decussation of the pyramids (fig 43, page 72). 

2. The POSTERIOR MEDIAN FISSURE continuous 
with the posterior median fissure of the spinal cord, 
expands above into the shallow rhomboidal space 
the floor of the 4th ventricle along the centre 
of which runs a mesial groove, in a line with, though 
not a direct continuation of, the median fissure of the 
cord. External to the posterior median fissure of 
the medulla are two minor sulci the paramedian 
and lateral dorsal, (see figs. 44, 45, page 72). 



FIG. 43 



2 n. optic 
Optic chiasma 
Optic t/act 



Medulla. 



Tuber cinereum 
infindibulvm 

Corpora 
mammillaria 



Pedunculi 
cerebri 
Lateral 
fillet 
Brachi 
pan 




PLATE XI. 



Colliculi ant. 
and post 

Brachia 
conjunctiva 
Locus, 
ceeruleus 

Fasc teres 
Super fovea 

Stria: 
iedullares 



Crossed pyramidal 
tract 



median 
fiss. 

Direct pyramidal 



Restiform body 
Tubercle Rolando 

Cuneate tubercle 
Clava 

Fasc. Rolando 
Fasc. cuneatus 
Fasc. gracilis 
Lat. dorsal f. Paramedian f. 



tract 



FlG. 45 



Left half 
valve of Vieusssens 



Striae 
ntedullares 

Olive 




Pedunculi 
cerebri 



Lateral 
fillet 



FIG. 46 



Fasc. gracilis 
Fasc. cuneatus 
Fasc. Rolando 

Paramedian f. 



Arci/'o-rtn 
fibres 

Restiform body 



Tubercle Rolando 
Cuneate tubercle 
Clava Ant. area 



Dorso-spino- 
<:erebellar tract 



Lat. dorsal J. 




Brachia 
pvntis 



Exter 
arciform fibres 



Antero-lat. fT^ Postero-lat. f. 



M* I.gn A rumauag. K 



73 

3- The LATERAL FISSURES antero - lateral and 
postero lateral are continuous with the lateral fissures 
of the cord. They give origin to the roots of the Qth 
loth, iith, and I2th pairs of cranial nerves the 
pth, loth, and iith pairs, springing from the con- 
tinuation of the postero-lateral groove, and the I2th 
pair from the continuation of the antero-lateral groove. 



2. WHITE MATTER OF THE MEDULLA. 
(Areas, Columns or Pyramids of the Medulla). 

By means of the above fissures the surface of 
each half of the medulla is marked out into three 
areas, viz. an anterior area, column or pyramid, between 
the anterior median fissure and the line of origin of 
the 1 2th cranial nerve; a lateral area, column or 
pyramid, between the I2th cranial nerve in front and 
the 9th, loth, and nth cranial nerves behind; and a 
posterior area, column or pyramid, between the posterior 
median fissure and the 9th, loth, and nth pairs of 
cranial nerve-roots. We shall now describe these 
several areas (figs. 43 to 46, page 72). 

i. The Anterior Area, also called the anterior 
column or pyramid of the medulla, lies between 
the anterior median fissure and the roots of the 
hypoglossal nerve, which serve to separate it from the 
olivary body. It is a pear-shaped prominence, which 
is broader above than below, though it becomes slightly 
constricted before disappearing beneath the lower 
border of the pons. It is streaked transversely by 
the external arciform fibres. To its constitution you 
will require to give your closest attention, for it is some- 



74 THE CENTRAL NERVOUS SYSTEM 

what complicated, and of the greatest importance 

( fi g- 93 P a g e 222 )- 

The anterior column of the spinal cord, you will 
remember, had (i) a median division, direct pyramidal 
tract, and (2) a lateral division -fasciculus proprius 
anterior. 

(i) Now the anterior pyramids of the medulla are, 
to a small extent only, made up of the fibres of this 
inner division direct pyramidal tract of their own 
side of the cord ; by far their greater part is composed 
of fibres crossed pyramidal tract which belong to 
the opposite lateral column of the spinal cord. For 
after leaving the cerebrum of its own side, this crossed 
tract descends through the anterior pyramid of the 
medulla of that side, where it forms the inner and 
by far the larger portion of that pyramid, the 
outer and smaller division of that same pyramid 
being composed of the corresponding direct pyramidal 
tract of that side. Leaving the anterior pyramid 
of the medulla, the fibres of the crossed pyramidal 
tract now decussate at the bottom of the anterior 
median fissure of the medulla with a similar set of 
fibres from the other side, thus forming the decussation 
of the pyramids from which the fibres travel through 
the anterior commissure of the spinal cord to the 
lateral column of the opposite side to that at which 
they left the cerebrum. Thus, for example, the LEFT 
ANTERIOR PYRAMID of the medulla is chiefly made 
up of the fibres of the crossed pyramidal tract on their 
way to the RIGHT LATERAL COLUMN, and, to a much 
smaller extent, by those of the direct pyramidal and 
uncrossed lateral pyramidal tracts of its own side. We 
must, however, again note that although the fibres of 



BRAIN, MEDULLA, WHITE MATTER 75 

the direct pyramidal tract do not decussate in the 
medulla, they do decussate, at different levels, as they 
pass down the spinal cord, and, ultimately, through 
the nerve-cells of the anterior horn, become connected, 
like the crossed tracts, with the anterior nerve-roots 
of the opposite side to that at which they left the 
cerebrum. 

The pyramidal tracts are the chief motor strands, 
and their decussation explains the phenomena of 
certain forms of paralysis, in which when one side of 
the brain, say the left, is injured above the level of the 
medulla, loss of motion ensues not on that side, but on 
the opposite side of the body to that on which the 
injury has been inflicted. " In cases, then, in which 
we find total or partial paralysis of the muscles on one 
side, with increased excitability to mechanical stimuli 
and a tendency to oontracture, we can justly conclude 
that the opposite pyramidal tracts are affected " 
(Ediiiger). 

(2) The lateral division of the anterior column of 
the spinal cord fasciculus proprius anterior consists 
either iw endogenous fibres, i.e. fibres confined to the 
spinal cord ; or of fibres which on reaching the medulla, 
are connected with a fine network of fibres, the formatio 
reticularis ; or with the anterior and posterior longi- 
tudinal bundles, two strands blended together at this 
level, but separate and distinct at higher levels (see page 
10 1, paglaS;, also figs. 52, 53, 54 page 96). 

2. The Posterior Area. This pyramid or column. 

* " 

lying between the posterior median fissure and the line 
of origin- of the Qth, loth, and nth cranial nerve-roots, 
may be divided into an upper or anterior part, and a 
lower or posterior part. The upper portion of this area 



76 THE CENTRAL NERVOUS SYSTEM 

enters into the formation of the lower half of the floor 
of the 4th ventricle, a cavity which should naturally be 
described at this stage, but owing to the fact that many 
of its parts are connected with the pons and with the 
cerebellum, its description must be deferred until we 
have treated of those portions of the brain (page 1 19). 

The lower portion of the posterior area, very 
similar in appearance to the spinal cord, is, for the 
most part, formed by the upward prolongation of the 
various white tracts of the posterior columns of the 
cord, the several strands there defined changing, when 
they reach the medulla, their position, their arrange- 
ment, and their names. These changes will be described 
below. There are, however, on this aspect of the 
medulla, two other strands, known respectively as the 
FASCICULUS of ROLANDO and the RESTIFORM BODY, 
which are not represented on the surface of the 
posterior column of the spinal cord, .for the former 
is chiefly grey matter, and the latter belongs mainly 
to the lateral column. 

We must now consider the changes referred to 
above : 

(i) FASCICULUS GRACILIS. In dealing with the 
white substance of the posterior column ^L the 
spinal cord, you will doubtless remember, 
called your attention to the existence, in the 
region, of a strand of fibres close to the posterior median 
fissure, called the fasciculus of Goll. Traced into the 
medulla, this strand, which lies between the posterior 
median and the paramedian fissures, becomes more 
prominent, and at the point where the central canal of 
the spinal cord becomes the cavity of the 4th ventricle, 




BRAIN, MEDULLA, WHITE MATTER 77 

the fasciculus enlarges, and is removed a little to one 
side. It is called the FASCICULUS GRACILIS slender 
bundle, and its enlarged upper end is known as the 
CLAVA the club, (figs. 44, 45, page 72). When followed 
upwards this club tapers to a point and becomes 
gradually lost, though we shall afterwards be able 
to trace its fibres, along with those of the next bundle, 
first to collections of grey matter nucleus gracilis and 
nucleus cuneatus in the medulla, and thence, by new 
strands of fibres, to the cerebrum and cerebellum (see 
Restiform body page 78 and Sensory Decussation and 
Fillet, page 89). 

(2) FASCICULUS CUNEATUS. The outer division of 
the posterior column of the spinal cord the cuneate 

fasciculus or fasciculus of Burdach passes into the 
medulla under the former name. It lies between 
the paramedian and the lateral dorsal sulci, and 
expanding above into a tubercle the CUNEATE 
TUBERCLE reaches upwards beyond the clava, and 
forms one of the lateral boundaries of the lower part 
of the 4th ventricle (fig. 45, page 72). 

(3) FASCICULUS OF ROLANDO. This tract, of a 
greyish colour, for there is little or no white matter on 
its surface, lies outside the fasciculus cuneatus, be- 
tween it and the line of origin of the roots of the pth, 
loth, ..and nth cranial nerves. Like the two tracts 
previously mentioned it expands above into a tubercle 
the tuberculum cinereum or TUBERCLE of ROLANDO. 
(% 45. P a g e 7 2 )' It is the continuation upwards of 
the substantia gelatinosa of Rolando of the spinal 
cord, and the white matter on its surface is the spinal 
root of the 5th cranial nerve. The fasciculus of 
Rolando, though often very poorly developed in the 



78 THE CENTRAL NERVOUS SYSTEM 

adult brain, is always well marked in the medulla of the 
child. 

(4) The RESTIFORM BODY. The remaining promin- 
ence, the largest and most conspicuous on this surface 
of the medulla, is called the INFERIOR CEREBELLAR 
PEDUNCLE or RESTIFORM BODY restis, a rope (figs. 44, 
45, page 72). Placed behind, and to the outer side of 
the lateral column of the cord, it lies above the level of 
the clava, of the cuneate tubercle, and of the tubercle 
of Rolando, and, when looked at from the surface, 
seems to be incorporated with these fasciculi, though 
not so in reality, for, as we shall presently see, it is 
composed of fibres derived, for the most part, from the 
lateral column of the spinal cord (fig. 45, page 72). 

On this area of the medulla, then, we note four 
strands (a) the fasciculus gracilis and its clava ; () the 
fasciculus cuneatus and its tubercle ; (c) the fasciculus 
of Rolando and its tubercle, and (d) the restiform body. 

3. The Lateral Area, pyramid or column of the 
medulla, continuous with the lateral column of the cord, 
lies between the roots of the hypoglossal nerve in front 
and those of the 9th, loth, and iith cranial nerves 
behind. It is wider below than above, where it is 
partially hidden from view by the oval eminence the 
Olivary Body. To determine the origin of its various 
strands we must refer back to the constitution of the 
corresponding column of the spinal cord. In that 
column we traced eight tracts the crossed and un- 
crossed pyramidal, the pre-pyramidal, the dorso-spino- 
cerebellar, the olivo - spinal tract, the ascending and 
descending antero-lateral tracts, and the fasciculus 
proprius lateralis. Of these strands (i) the crossed and 
(2) the uncrossed pyramidal have already been traced, 



RRAIN, MEDULLA, WHITE MATTER 79 

the former from the anterior pyramid of the opposite 
side, the latter from the anterior pyramid of its own 
side ; (3) the dorso-spino-cerebellar or lateral cerebellar 
tract, on the other hand, reaches the posterior area of 
the medulla. Commencing in the lateral column of the 
spinal cord, from the cells of Clarke's column, it forms 
a superficial band of fibres which runs upwards and 
backwards across the line of origin of the Qth, loth and 
nth cranial nerves, over the fasciculus of Rolando, and 
above its tubercle (fig. 45, page 72). It then crosses 
the cuneate fasciculus, and, turning sharply upwards, is 
joined by a set of fibres the external arciform fibres 
which, together with it, constitute the main mass of the 
restiform body or inferior peduncle of the cerebellum, 
seen on the posterior area of the medulla (figs. 44 and 
45, page 72, and fig. 79, page 188). The five remaining 
tracts of the lateral column of the spinal cord are found 
in the lateral pyramid of the medulla thus (4) the 
ascending antero- lateral or Cowers' tract, composed of 
the ventro-spino-cerebellar, the spino-thalamic, and the 
spino-tectal ; and (5) the prepyramidal or rtibro -spinal 
tract, lie in the groove behind the olive (fig. 49, page 84) ; 
(6) the descending antero-lateral tract (Lowenthal) is 
found in the groove in front of the olive ; (7) the olivo- 
spinal is dorsal to it ; whereas (8) the fasciculus proprius 
lateral is goes to the formatio reticularis, some of its 
fibres passing on the superficial, some on the deep 
surface of the olivary body. 

Thus, then, the fibres of the lateral column of the 
spinal cord, on reaching the medulla, are disposed of 
in three ways : (a) Some the crossed and uncrossed 
pyramidal tracts are found in the anterior pyramid of 
the same or of the opposite side, as the case may be ; 



8o THE CENTRAL NERVOUS SYSTEM 

(b) others dorso-spino-cerebellar tract go to the 
restiform body, and thence to the cerebellum of the 
same side ; (c) others the ascending and descending 
antero - lateral tracts, the prepyramidal tracts, and 
the fasciculus proprius reach the lateral area of the 
medulla, passing partly behind, partly in front, partly 
superficial to, and partly beneath the olive to the 
formatio reticularis (fig. 49, page 84). The constitution 
and ultimate destination of these strands of fibres will 
be seen on page 88 after we have treated of the grey 
matter of the medulla, for, at present, you would not 
understand the description. 

Olivary Body. The olivary body is the oval 
prominence, about half-an-inch long, placed at the 
upper end of the lateral area of the medulla. It is 
bounded in front by the roots of the I2th cranial nerve, 
but is separated behind from those of the 9th, loth, and 
nth cranial nerves by a narrow white tract, which is 
part of the lateral column of the cord. The upper pole 
of the olive, almost touches the lower border of the 
pons ; its lower pole is crossed transversely by delicate 
fibres the external arciform fibres, which, at the 
present stage of their course, are seen to emerge from 
the anterior median fissure of the medulla, and, after 
crossing over the surface of the anterior and lateral 
pyramids, and over the lower part of the olives, finally 
turn upwards, along with the lateral cerebellar tract, to 
form, with it, part of the restiform body (figs. 43, 45, 
46, page 72). The arcuate fibres will be again referred 
to in treating of the grey matter of the medulla (page 9 1 ). 
If you now cut into one of the olives you will find that 
it contains a grey core, called the corpus dentalum or 
inferior olivary nucleus (see fig. 49, page 84). 



BRAIN, MEDULLA, OLIVARY BODY 



CRANIAL NERVES. Besides the various longitudinal 
tracts which have been engaging our attention, there 
are, in this part of the medulla, several strands of 
nerve-fibres which traverse the medulla from behind 
forwards. They are the fibres of the 8th to the I2th 
cranial nerves, which are on their way from their 
deep to their superficial origins, or vice versa (fig. 49, 
page 84). See also Cranial Nerves, page 197. 

TABLE OF OBJECTS SEEN ON SURFACE OF MEDULLA. 

( Anterior median, with decussation of the pyramids. 
Posterior median, which widens out into the 4th 
ventricle. 

Antero-lateral, with the roots of the 

1 2th cranial nerve. 

Postero-lateral, with the roots of the 
9th, loth and nth cranial nerves. 
( Decussation of pyramids. 
I External arcuate fibres. 
fOlive. 

External arciform fibres. 
Tracts of white matter in 

relation to the olive. 
Restiform body. 
Fasciculus of Rolando and 



Sulci 

or 
Fissures. 



Two lateral 



I. Anterior. 



2. Lateral. 



Areas 

or 
Pyramids 

or its tubercle. 

Columns. < Fasciculus cuneatus and 

Posterior. <; its tubercle. 

Fasciculus gracilis and its 

clava. 

Upper f Lower half of the floor of 
part. \ 4th ventricle. 

SUMMARY. From the above description you will 
see that the medulla forms an elongated, inverted, 
truncated, fluted, four-sided cone ; that its surface is 
lined by four fissures, an anterior, a posterior, and two 



82 

lateral with their nerve-roots : that it has three areas an 
anterior, with is pyramids and their decussation ; a 
lateral, with its olive; a posterior, with its fasciculus 
gracilis, fasciculus cuneatus, and fasciculus of Rolando, 
and their respective enlargements ; and, finally, the 
restiform body or inferior cerebellar peduncle. 

TABLE OF RELATIONS BETWEEN WHITE TRACTS OF CORD 
AND THEIR REPRESENTATIVES IN THE MEDULLA. 

Cord. Medulla. 

c r ( from the outer part of the an- 

3 I. Direct pyramidal tract -( terior pyramid of the 

medulla of the same side. 

anterior and posterior longi- 
Fasc.culus proprms 



I formatio reticularis. 
** ( f from the inner part of the 

1. Crossed pyramidal tract j anterior pyramid of the 

I opposite side. 

2. Uncrossed lateral pyra- ( from anterior pyramid of its 

midal tract 1 own side. 

3. Dorso- spino- cerebellar f to restiform body and thence 

or lateral cerebellar { to the cerebellum of same 
j tract I side. 

4. Antero-lateral ascending ~\ 

tract of Cowers (ven- to the cerebrum and cere- 
tro- spino -cerebellar, | bellum probably crossed 
spino -thalamic and I sensory tract, 
spino-tectal) J 

4 5. Prepyramidal or rubro- \ t o lateral pyramid, 
spinal tract ) 

)from nucleus of the vestibular 
division of the auditory 
nerve, through the cere- 
bellum. 

7. Fasciculus proprius later- f to or from formatio reti- 
alis I cularis. 



BRAIN, MEDULLA, GREY MATTER 83 

_ . . ... ,,, m r to fasciculus gracilis and its 

I. Fasciculus gracihs (Goll) 



nuc i eus . 

2. Fasciculus cuneatus f to fasciculus cuneatus and 
(Burdach) \ to its nucleus. 

f to the grey matter of the 

posterior horn. 

4. Fasciculus proprius f to or from formatio reti- 
posterior I cularis. 



3. GREY MATTER OF THE MEDULLA. 

From the white strands of the medulla, which 
have so far occupied our attention, we next turn to 
the consideration of the arrangement of its grey 
substance. This is much more irregular than that of 
the spinal cord, and for its satisfactory study you 
will require a special series of preparations, though 
the accompanying figures, page 84 will no doubt give 
you material assistance. 

The grey matter of the medulla oblongata may 
be described under two heads (i) that represented 
in the spinal cord, and derived from or replacing 
one or other of its grey crescents ; (2) that not so 
represented, but forming isolated collections or nuclei 
not obviously connected with the grey matter of the 
spinal cord. 

i. Grey Matter replacing 1 the Grey Crescents. 
Transverse sections of the lower part of the medulla 
will show you that its grey matter has an arrangement 
very similar to that of the grey matter of the spinal 
cord ; but that, higher up in the medulla, the appear- 
ance of the grey crescents becomes much changed 
(compare fig. 47, page 84, with figs. 8, etc., page 14). 

(a) The anterior cornu of the spinal cord, as we 
trace it upwards, loses its characteristic shape, for, 



84 THE CENTRAL NERVOUS SYSTEM 

owing to the fact that the fibres of the crossed 
pyramidal tract, in their course from the medulla to 
the lateral column of the cord, must, of necessity, cut 
their way through the neck of the anterior horn, the 
head of that horn becomes severed from the base. 
The head of the horn, thus detached, enlarges, and, 
by the interposition of the anterior pyramids between 
it and the anterior median fissure, is pushed from the 
antero-lateral aspect of the cord to the lateral aspect of 
the medulla, where, in sections of the lower part of the 
medulla, it may be seen as a distinct collection of 
nerve-cells, the NUCLEUS LATER ALIS (fig. 48, page 84). 

Again, when the central canal of the spinal cord 
opens out to form the floor of the 4th ventricle, the grey 
matter which surrounds that canal is brought to the 
surface, and hence the -base of the anterior horn 
appears on the ventricular floor as a narrow, grey tract 
close to the median furrow (figs 47, 48, and 49, page 
84), where it now forms the NUCLEUS of the HYPO- 
GLOSSAL NERVE. In sections of the medulla at this 
level the nerve may be seen as a band of fibres 
running from the nucleus towards the anterior surface 
of the medulla (fig. 49, page 84). Close to this 
nucleus is another small collection of nerve-cells the 
nucleus of the fasiculus teres (fig. 49, page 84). 

The greater part of the anterior horn the neck 
is replaced by a reticulum of cells and fibres, part of 
these latter being the fibres of the crossed tract on 
their way from the opposite side of the medulla. This 
network constitutes the anterior part of the formatio 
reticularis (figs. 48 and 49, page 84). 

(b) The grey matter of the posterior horn, on 
reaching the medulla, also takes up a lateral position 



Transverse Sections of the Medulla. 

FIG. 47 
/W. median ^r^T ^ T . ^ Fasc. gracilis. 



PLATE XII. 



fi*. 




\ Substantia gelatin . 
\ Rolando. 



Decussation of 
pyramids. 



FIG. 48. 



' \ cuneatus 
Nucleus of llth n. 

Fasc. Rolando. 
Nucleus of 12th n. 
Nucleus of 
Rolando. 
Descending root 
of 9th and IQth nerve 
Nucleus 
lateralis. 

Olive 

Sensory decussation 
(fillet). 

Nucleus 
of 

,r , ... llth . 

Nucleus gractlts.^ 
Nucleus cuneatus. 

Fasc. solitarius.. 

Restiform body. 
Nucleus ambiguus. 
Formatio reticularis. 

]Qth nerve or vagus. ' 

Asc. antero-lateral tract. 

^bino-thalamic tmct. -^ / p. 

/ 
Rubro.-spinal tract 

t Accessory olive.'" 




Nucleus 
gracilis. 

\ Nucleus 
, cuneatus. 
.-Lateral cerebettar t 
Spinal root of 
5th nerve. 

-Rubro-spinal t. 

tract. 
Accessory olive. 



Arcuate 
nucleus. 




Nucleus offasc. 
teres. 



Descending 
ant. -lateral tract. 




External 
a rciform fibres. 



^.1'ost. long, bundle. 
Ant. lontj. bundle 

Spinal root of 
_ 5M nerve. 

- A rciform fibres. 
Nucleus lateralis. 
Fillet. 
Inferior olive. 

Fasc. proprius lot. 

\2th nerve or 
hypoglossal nerve. 
Ant. pyramids 
< if medulla. 

'.>.' Lfr, * Cur..n; Kdio' 




BRAIN, MEDULLA, GREY MATTER 85 

and increases in amount. The head of the horn, 
severed from the base by the sensory decussation, as 
the head of the anterior horn was severed by the motor 
decussation, is now much enlarged, and comes nearer 
to the surface. At about the middle of the medulla 
it appears as a well-marked nucleus, the NUCLEUS 
of ROLANDO (fig. 48, page 84), beneath the surface 
prominence called the tubercle of Rolando. To its 
outer side you will see a band of white fibres, the 
SPINAL ROOT Of the FIFTH CRANIAL NERVE (fig. 48, 
page 84). 

The grey matter of the base of this horn, also much 
increased in amount, lies between the median line 
and the grey nucleus of Rolando. In the medulla 
it is replaced by two superficial aggregations the inner 
one, beneath the fasciculus gracilis, forming the NUCLEUS 
GRACILIS ; the outer, which is in part an outgrowth 
of the posterior horn, beneath the fasciculus cuneatus, 
forming the NUCLKUS CUNEATUS (fig. 48, page 84). 
Each nucleus thus lies beneath and gives its name to 
the corresponding white tract on the surface, and 
causes the elevations called the clava and the cuneate 
tubercle. To these nuclei, as we know, can be traced 
most of the fibres of the posterior column of the spinal 
cord. The nuclei themselves may be followed as far as 
the pons. From them secondary sets of fibres 
the internal arciform fibres take their start and 
crossing the middle line, form the superior sensory 
decussation or the decussation of the fillet (see page 89). 

The neck of the posterior cornu, like that of the 
anterior, is replaced by a network of fibres, the white 
reticulum, which becomes continuous with the grey 
reticulum, constituting together the FORMATIO RETICU- 



86 THE CENTRAL NERVOUS SYSTEM 

LARIS, a network of longitudinal, oblique, and trans- 
verse fibres with nerve - cells and neuroglia - cells 
embedded therein (figs, 47, 48, 49, page 84). The fibres 
of this reticulum are chiefly commissural in nature but 
some of its longitudinal strands are derived from the 
mixed zones fasciculi proprii of the anterior and 
lateral columns of the spinal cord. 

2. Isolated Grey Masses or Nuclei of the 
Medulla. The chief of these nuclei are 

1. The corpus dentatum or olivary nucleus. 

2. The accessory olives. 

3. The arciform or arcuate nucleus. 
4. Nuclei of cranial nerves. 

(1) The CORPUS DENTATUM or olivary nucleus is 
contained in the centre of the olivary body, which 
must be cut into in order to see it. This ganglion 
consists of flask - shaped, multipolar nerve - cells, and 
neuroglia-cells arranged as an oval zigzag lamina or 
crumpled sheet of grey matter, concave and open on its 
inner aspect (fig. 49, page 84). Through this opening, 
called the hilum, the olivary peduncle, a bundle of 
nerve-fibres, enters into the centre of the olivary 
nucleus to be there distributed in different directions. 

The corpus dentatum or olivary ganglion is closely 
connected with a grey mass in the cerebellum the 
corpus dentatum of the cerebellum for any injury to 
this latter nucleus causes atrophy of the opposite 
olivary ganglion (fig. 79, No. 6, page 188). 

(2) Two other isolated nuclei the ACCESSORY 
OLIVES will be found, the one on the inner side of, the 
other behind, the corpus dentatum of the olivary body. 
They are linear in shape, and are closely connected 
with the olivary nucleus (fig. 49 page 84). 



BRAIN, MEDULLA, GREY MATTER 



The third nucleus ARCUATE NUCLEUS or nucleus 
of the external arcuate fibres (fig. 48, page 84) is 
placed amongst these fibres as they cross over the 
anterior pyramids of the medulla. It is continuous 
above with the nucleus pontis. 

(3) NUCLEI OF CRANIAL NERVES. The rest of 
the grey matter of the medulla consists of the nuclei 
of the 8th, 9th, loth, iith and I2th cranial nerves. It 
will be studied in relation to the floor of the 4th 
ventricle (page 124). 

TABLE OF GREY MATTER OF THE MEDULLA. 
Cord. Medulla. 

Head Nucleus lateralis. 

Neck Anterior part of the formatio 

reticularis. 

Base Nucleus of the hypoglossal nerve. 
Head Nucleus of Rolando. 
Neck Posterior part of the formatio 

reticularis. 
/ Nucleus gracilis. 
Base J Nucleus cuneatus. 

| Nuclei on floor of 4th ventricle. 
Nucleus of the olivary body. 
Accessory olivary nuclei. 
Nucleus of the external arciform fibres. 
Nuclei of cranial nerves, viz. 8th, gth, 
roth, iith, I2th. 

Raphe. A transverse section of the medulla will 
show you that, above the level of the pyramidal decussa- 
tion, the medulla is partially divided into two lateral 
segments by a central median raphe or partition, 
which forms a thin membranous septum of nerve- 
substance, extending from the anterior median fissure 
to beneath the central groove on the floor of the 
4th ventricle. It consists of numberless fibres which 





Anterior J 


Grey 


Cornu. | 


Matter 


V. 


of the , 




Spinal 
Cord. 


Posterior 




Cornu. 



Isolated Nuclei. 



88 THE CENTRAL NERVOUS SYSTEM 

run in various directions and which are interspersed 
with small collections of multipolar nerve-cells. 

WHITE STRANDS OF THE MEDULLA (continued 
from page 80). In the previous sections we have studied 
the arrangements of the grey matter of the medulla, and 
are now in a position to resume the tracing of the 
several white tracts which we left on page 80. 

Motor and Sensory Strands and their Deeussations. 

I. The MOTOR STRANDS direct and crossed, and 
their decussations, the one set in the spinal cord, the 
other in the medulla have already been sufficiently 
considered on page 74. The spinal crossings constitute 
the inferior motor decussations, or the crossings of the 
fibres of the direct pyramidal tracts; the medullary 
crossing, on the other hand, constitutes the superior 
motor or inferior pyramidal decussations, the crossing of 
the fibres of the crossed pyramidal tracts. 

II The SENSORY STRANDS and their decussations 
were mentioned on page 41. On that page we saw that 
the posterior nerve-roots, sensory in function and start- 
ing from the cells in the ganglia of the posterior nerve- 
roots, could, on entering the spinal cord, be traced to two 
chief cell-stations, the one situated in the spinal cord the 
cells of the posterior horn : the other in the medulla the 
cells of the nucleus gracilis and the nucleus cuneatus. 

i. ^\\Q fibres which end\\\ the spinal cord, in Clarke's 
columns, and in other cells of the posterior horn, are 
succeeded by four new strands, viz. : 

(a) The dorso-spino-cerebellar. 

(b) The ventro-spino-cerebellar. 

(c) The spino-thalamic. 
(d} The spino-tectal, 



BRAIN, MEDULLA, STRANDS, DECUSSATIONS 89 

Of the above four strands (a) the dorso-spino-cerebellar 
or direct lateral cerebellar tract, after leaving the cells 
of Clarke's column, keeps to its own side, and, by 
way of the restiform body, reaches the cerebellum of 
that same side (see page r 1 1 ). The other three strands 
which constitute Cowers' tract, cross the middle line 
in the anterior or white commissure, thus forming 
the inferior sensory decussation. From this decussation, 
(b] the ventro-spino- cerebellar ascends in the lateral 
column of the spinal cord, and reaches the medulla 
behind and lateral to the olivary body. On nearing 
the upper border of the pons it turns backwards on itself 
and descends to the cerebellum (see page 100). 

(c) The spino-thalamic tract, after crossing, ascends 
in the anterior and lateral columns of the spinal cord. 
In the medulla it lies behind the olivary body. In the 
pons it is joined by the bulbo-thalamic tract (see lemnis- 
cus or fillet, page 100). 

(d) The spino-tectal tract passes through the lateral 
part of the medulla behind the olive, and reaches the 
mid-brain (see page 101). 

2. ^hz fibres which end in the medulla, viz. the tracts 
of Goll and of Burdach, do not enter the grey matter 
of the spinal cord but go at once to the cells of the 
nucleus gracilis and of the nucleus cuneatus. From 
these nuclei new strands take their origin, and travelling, 
as arcuate fibres, from the dorsal to the ventral aspect 
of the medulla, come to lie in front of the central canal, 
thereby thrusting that canal towards the back of the 
medulla. Crossing in the middle line, above and behind 
the motor pyramidal decussation, they form the superior 
sensory or superior pyramidal decussation, the fibres of 
which, at first, radiate sideways from the mesial raphe\ 



THE CENTRAL NERVOUS SYSTEM 



but afterwards turn upwards, and, becoming longitudinal, 
form a well-marked strand, the bulbo-thalamic tract, 
which lies close to the middle line, behind the motor 
tracts. It forms the lemniscus or main fillet. In the 
pons it is joined by the spino-thalamic tract, from the 
cells of the posterior cornu, the two together forming the 
great crossed sensory route from the opposite posterior 
spinal nerve-roots to the cerebrum (see page 229). 

In all, then, we have four sets of decussations, two in 
the spinal cord, two in the medulla, two motor and two 
sensory. For clearness and easy reference they are given 
in the table below, arranged according to their positions 
and according to their functions. 

The other tracts, named on page 79, viz. the pre- 
pyramidal or rubro-spinal, the descending antero-lateral 
or Lowenthal's tract, and the fasciculus lateralis or 
mixed zone, will be considered at a later stage (see 
pages 1 88, 208). In the medulla they are found either 
in the groove in front of the olive, or in the one behind 
it, or in both. 

TABLE OF DECUSSATIONS SENSORY AND MOTOR. 



Spinal decussations. 



Medullary decussations. 



1. Inferior Sensory the decussation 

of the three strands of the ascend- 
ing antero-lateral tract or Cowers' 
tract. 

2. Inferior Motor the decussations 

of the direct pyramidal tracts. 

1. Superior Sensory superior pyra- 

midal -decussation of the fillet or 
better of the bulbo-thalamic section 
of that tract. 

2. Superior Motor inferior pyramidal 

the decussation of the crossed 
pyramidal tracts. 



PLATE XIII. 



FIG. 50 



r- if* / i an ?- 

C olliculi 1 . . 

( post. 

Nucleus of An 
Nucleus of 4 n 
Locus c<znileiis 
Desc. root 5 n 



r / Motor 
1 ( Sensory 

Nucleus 6 n. 
7. 




Spinal-root 
of 5th n. 



Nuclei of Floor of th Ventricle. 



FIG. 51 



Spinal root 12 n . 9n. 10 .!!. 8 M . 4 n. 




7 n. 6 n. 



. Descending 
root o/5n. 



U* L|n A CuM,u.g. Kdmbu 



BRAIN, MEDULLA, ARCUATE FIBRES 91 

Arcuate or Areiform Fibres- These fibres have 
been several times alluded to, so that we shall now 
merely collect together the statements previously made. 
They can be divided into a superficial or external set 
and a deep or internal set. 

1. THE SUPERFICIAL ARCUATE FIBRES form two 
groups, an anterior external and a posterior external. 

(a) The anterior external arcuate fibres mostly spring 
from the cells of the nucleus gracilis and the nucleus 
cuneatus of the posterior area of the medulla. From 
these nuclei the fibres sweep forwards towards the 
ventral aspect of the medulla, and decussating in the 
mesial raphe, emerge from the anterior mesial fissure, 
and wind round the anterior pyramid of the opposite 
side to that at which they started (fig. 46, page 72). 
They next cross, in order, the olives, the surface of the 
lateral pyramid below the olives, and the line of origin 
of the Qth, loth and nth cranial nerves, and, turning 
upwards, blend with the fibres of the dorso-spino- 
cerebellar tract to form part of the restiform body (fig. 45, 
page 72). 

(b} The other group the posterior external arcuate 
fibres having the same source as the previous set, 
passes from the posterior column of one side to the 
restiform body of the same side (fig. 79, Nos. 4 and 5, 
page 1 88). 

2. The DEEP ARCUATE FIBRES are a delicate net- 
work of fibres found between the olives and behind 
the pyramids. Their exact course and origin are, in 
many cases, unknown. Some of them are derived from 
the nuclei of the posterior columns before mentioned, 
and form the superior pyramidal or superior sensory 
decussation. Others enter the centre of the olivary 



92 THE CENTRAL NERVOUS SYSTEM 

nucleus through its hilum ; and either join the cells of 
that nucleus, or pass through the nucleus to the resti- 
form body directly, or first make to the surface, and 
then go, along with the external arciform fibres, to the 
restiform body. Others, again, are connected with the 
nuclei of the sensory cranial nerves, or with the cells of 
the formatio reticularis. 

Recapitulation. Since the constitution of the 
medulla is so complicated, it will be well to summarise 
the above facts in a somewhat different order. If we 
examine a section of the medulla such as that shown 
in fig. 49, plate xii., page 84, we shall find that the 
strands of nerve-fibres which constitute the 9th, loth, 
nth, and I2th cranial nerves, as they traverse the 
medulla from their deep to their superficial origins, 
divide each half of the medulla into three triangular 
areas (i)one, anterior, between the anterior mesial fissure 
and the fasciculi of the I2th cranial nerve; (2) one, 
lateral, between the fasciculi of the I2th cranial nerve and 
those of the 9th, roth, and nth cranial nerves; and (3) 
one, posterior, between the fasciculi of the last-named 
nerves and the posterior mesial fissure. 

i. Anterior Area. In this area, commencing at 
the anterior mesial fissure, we meet with (a) the 
ANTERIOR PYRAMIDS of the medulla (fig. 49, page 84), 
composed of three sets of longitudinal fibres viz. the 
crossed pyramidal tracts going to the opposite lateral 
columns of the cord ; and the direct and uncrossed 
pyramidal tracts on their way to their own side of the 
cord. Most of the motor fibres coming from the brain 
are contained in these pyramids, though others first go 
to the pons, thence to the cerebellum, thence to spinal 
cord. 



BRAIN, MEDULLA, RECAPITULATION 93 

(b) Crossing the anterior pyramids transversely are 
a set of fibres, the superficial arcuate, which, having 
their origin in the nucleus gracilis and nucleus cuneatus 
of the one side of the medulla, decussate in the middle 
line, and emerge from the anterior median fissure. 
Crossing over the surface of the anterior and lateral 
pyramids of the medulla, and over the olives of the 
opposite side to that from which they started, they go 
to join the restiform body. Amongst these arcuate 
fibres is a mass of grey matter, the NUCLEUS ARCUATUS 
(fig. 48, page 84). 

(c) In the middle line behind the pyramids, between 
them and the central canal, are thick, white bundles of 
fibres arranged in concentric curves deep arcuate fibres 
which also spring from the region of the posterior 
columns, from the two nuclei gracilis and cuneatus. 
They form the SUPERIOR PYRAMIDAL or SUPERIOR 
SENSORY DECUSSATION, or decussation of the fillet 
(fig. 48, page 84). Higher up in the medulla this same 
region is occupied by fibres which traverse the medulla 
in all directions formatio reiicularis. Neuroglia-cells 
and a few nerve-cells are scattered amongst the fibres. 
Within this network are three longitudinal strands, the 
FILLET or LEMNISCUS and the ANTERIOR and POSTERIOR 
LONGITUDINAL BUNDLES (figs. 48, 49, page 84). 

2. Lateral Area. Outside the formatio reticularis, 
between it and the surface, but behind the pyramids, 
is the (a) OLIVARY NUCLEUS (fig. 49, page 84) with the 
OLIVARY PEDUNCLES. This nucleus is covered super- 
ficially by the external arciform fibres, (b) Close to 
it are the ACCESSORY OLIVES (fig. 49, page 84). (c) 
Behind the olives lies the NUCLEUS LATERALIS (fig. 48, 
page 84), the upward continuation of the anterior cornu 



94 THE CENTRAL NERVOUS SYSTEM 

of the spinal cord, (d) Ventral to the olive is the 
DESCENDING ANTERO-LATERAL or Lowenthal's tract, 
and dorsal to it are (e) the ASCENDING ANTERO-LATERAL 
or tract of Cowers, and (/) the PREPYRAMIDAL or RUBRO- 
SPINAL TRACT (fig. 49, page 84). 

3. Posterior Area. Posterior to the nucleus lateralis 
appears (a) the grey TUBERCLE of ROLANDO (fig. 48, 
page 84), the enlarged head of the posterior horn of the 
spinal cord. On its outer side lies the SPINAL ROOT 
of the 5th CRANIAL NERVE (fig. 48, page 84). (ft) 
Superficial to the tubercle of Rolando are the fibres 
of the DORSO-SPINO-CEREBELLAR or LATERAL CERE- 
BELLAR TRACT, which are on their way, along with the 
arciform fibres, to the inferior cerebellar peduncle or 
restiform body, (c) Posterior and internal to the nucleus 
of Rolando is a mass of grey matter the NUCLEUS 
CUNEATUS (fig. 48, page 84) lying beneath the cuneate 
tubercle ; and still nearer the middle line, (d) the 
NUCLEUS GRACILIS, lying beneath the clava (fig. 48, 
page 84). 

In front of the nucleus cuneatus will be seen a 
special, white, rounded fasciculus, known as (e) the 
FASCICULUS SOLITARIUS (fig. 49, page 84), formed, in 
part, by the descending root of the glosso-pharyngeal 
nerve. 

Close to the middle line, internal to the nucleus 
cuneatus, lies (/) the NUCLEUS of the HYPOGLOSSAL 
NERVE from which the nerve itself may be seen running 
forwards to its superficial origin. 

The rest of the grey matter, seen on each side of 
the posterior median groove, internal to the nucleus 
gracilis, belongs to the floor of the 4th ventricle. It 
will be fully described with that cavity (page 124). 



BRAIN, PONS VAROLII 95 

The next division of the brain to be considered is 
the metencephalon, comprising the pons and cerebellum. 

II. PONS VAROLII. 

(Figs. 43 and 46, Plate XI. Page 72.) 

GENERAL OUTLINE. The Pons Varolii part of the 
metencephalon, the other part being the cerebellum- 
is the broad, white band, about an inch in depth and in 
thickness, which crosses transversely between the two 
halves of the cerebellum. It lies below the level of the 
crura cerebri and above the level of the medulla (fig. 43, 
page 72). In front it rests on the slope formed by the 
basi-occipital and the basi-sphenoid ; behind it is hidden 
by the cerebellum. Composed of grey and white 
matter, it can be divided into a central portion or body, 
and two lateral prolongations or peduncles. 

(i) The Body has four surfaces anterior and pos- 
terior ; superior and inferior. The anterior surface, 
quadrilateral in outline, is convex from side to side, and 
slightly so from above downwards. It is limited above 
and below by the corresponding borders. Striated 
transversely it presents along the middle line, a shallow, 
vertical groove, the basilar groove, which lodges the basilar 
artery. On each side of this groove runs a longitudinal 
elevation, due to the passage downwards of the pyra- 
midal tracts on their way to the medulla. 

Of the borders, both of which are transverse, the 
upper, which marks off the pons from the crura cerebri, 
is arched at the sides but slightly depressed or notched 
in the middle line. At this border you will find two 
pairs of cranial nerves, the 3rd nerves on the mesial 
side of the crura, the 4th nerves on the lateral side. 

The lower border marks the limit between the pons 



96 THE CENTRAL NERVOUS SYSTEM 

and the medulla. It is in contact with the upper ends 
of the pyramids, but is separated from the upper poles 
of the olives by a slight interval. Three pairs of cranial 
nerves appear at this border, which, named from within 
outwards, are the 6th nerves, situated a short distance 
from the middle line, and further out, the 7th and 8th 
cranial nerves (fig. 43 page 72). 

The posterior surface of the body has ill-defined 
limits, being continuous below with the medulla and 
above with the crura cerebri. Flattened from before 
backwards and expanded from side to side, it forms 
the upper division of the floor of the 4th ventricle 
(see page 1 1 9). 

The upper and lower surfaces only become visible 
when we make transverse sections at the levels of 
the corresponding borders. They are continuous on 
the one hand with the medulla, on the other with the 
cerebral peduncles. 

(2) The Peduncles, the lateral prolongations of the 
body, form the brachia pontis or middle peduncles of 
the cerebellum. They are two rounded bands, right 
and left, narrower than the body, for they are com- 
pressed from above downwards. The line of demarca- 
tion between them and the body of the pons is purely 
artificial, being indicated by lines drawn vertically 
through the points of attachment of the 5th cranial 
nerves, which you will see springing, one on each side, 
from this aspect of the pons. 

The middle peduncles carry fibres to the cerebellum 
from the nucleus pontis of both the right and left sides. 
It is interesting to note that, in mammalia, the size of 
the pons bears a direct relation to the size of the lateral 
lobes of the cerebellum, and that in birds, in reptiles 



FIG. 52. PLATE XIV. 

Transverse Section through the middle of the Pons Varolii. 

. {. .}ParS intermedia. 
Nucleus of -\^^^^^^^^^^^^^f^^^^^^ r-^. 

Sthnen-e. ^^L^. -**..-. !: ( - V -Kestiform body. 

Nucleus of. /, *r /$'''..-'<:''' ^^Post longit. 

ftth nerve. *.,^ ' - ' \' ... bundle 

int. longit. bundle *3^<JSfc& '^.Asc. root of 

Superu^ive^/^ . *'* 

- ^?~PT^. * ^-^-- r , r- ' Filut - 

Trapezium.- ^ ^^ 

&th netve. 




Pyramidal 
tracts. 



1th nerve. 



'Qth nerve. 
FIG. 53. 

Transverse Section of upper part of Pons. 

Valve of ~~~ 

l rackia conjuctiva. 
Desc. root of 5th neive. 



Locus caeruletis 
Formatio 
reticularis 



Spino-thalamic. t. 
Ventro-spino - 
cerebellar. t. 
Spino-tectal 
5th nerve., 

Nucleus 
Pontis. 




Post, lonpit. bundle. 
Ant. long, bundle 



mesial} 

Gvaiers' tract. 



longitudinal 
tracts. 






FIG. 54. 
Transverse Section of Pedunculi Cerebri. 

Colliculi anttriores. 
Rubro-spinal __ 

Aquoeductus cerebri. 
Lateral} 



( lateral. 
Fillet 

I mesial. 



Nucleus of 
3/rd nerve 



Post, longit. 
fascic. 

Ant. longit. 
fascic. 



'esial) 




Fillet. 



Temporo-occipito - 
pontine tract. 



Nucleus 
ruber Kubro- 
sp-tnal tract 



3rrf nerve.* 

Fnmto- 
pontine tract. 



Substantia 
nigra. 

-Caudate ctrebellar 

tract. 
Pyramidal tracts. 

Geniculate fascic. 



BRAIN, PONS, CONSTITUTION 97 

and in fishes, where we have no cerebellar hemispheres, 
the pons is also wanting.- 

CONSTITUTION OF THE PONS. When we examine 
transverse sections of the pons we find that it can be 
divided into two portions a denser or ventral part 
pars bast/arts : and a looser or dorsal part pars dorsalis. 
The latter, also called the tegmentum, is made up of 
constituents derived from the spinal cord and medulla, 
with the exception of the pyramidal tracts. The former, 
or ventral part, besides the proper fibres of the pons, con- 
tains the prolongations of the pyramids of the medulla. 

We shall study the constitution of the pons according 
to the following table : 

TABLE OF THE CONSTITUTION OF THE PONS VAROLII. 

I White Matter of the Pons. 

1. Transverse fibres. 

(1) Superficial. 

(2) Deep corpus trapezoideum. 

2. Longitudinal fibres. 

(1) Superficial. 

( Direct. 
(a) Pyramidal tracts . -| Crossed. 

\ Uncrossed. 

{Fronto-pontine. 
Temporo-pontine 
Occipito-pontine. 

(2) Deep. 

(a) Lemniscus or fillet . I Mesia1 ' main Or U PP er fillet " 

( Lateral, accessory or lower fillet. 

(b} Antero-lateral ascending (Cowers) (ventro-spino-cerebellar, 
spino-thalamic and spino-tectal). 

(c) Rubro-spinal or prepyramidal. 

(d) Longitudinal bundles ( Dorsa1 ' P oslerior or mesial - 

( Ventral, anterior or tecto-spinal. 

(e) Fasciculus teres. 
(/) Olivary fasciculus. 

H 



98 THE CENTRAL NERVOUS SYSTEM 

(3) Fibres of Cranial Nerves The 5th cranial nerve with its 

descending root, and fibres of the 6th , yth, and part of the 
8th cranial nerves. 

(4) Formatio reticularis. 

(5) Raphe. 

II. Grey Matter of the Pans. 

1. Nucleus pontis. 

2. Superior olive and accessory olives. 

3. Substantia gelatinosa of Rolando. 

> 4. Nuclei of origin of 5th, 6th, 7th, and 8th cranial nerves. 
5. Locus caeruleus. 

1. WHITE MATTER OF THE PONS. 

DISSECTION. To see the arrangement of the white fibres of 
the pons, you will require to dissect down on each side of the 
middle line, through the superficial fibres, until you reach a 
longitudinal set passing upwards and downwards. Reflect the 
longitudinal fibres, when a deeper transverse group will come 
into view. 

The white or medullated nerve-fibres of the pons are 
arranged in two sets, a transverse and a longitudinal, 
each being again divisible into a superficial and a deep 
group. 

i. Transverse Fibres. (i) The SUPERFICIAL TRANS- 
VERSE fibres appear on the ventral surface of the pons, 
and (2) the DEEP TRANSVERSE fibres lie behind and 
between the superficial and deep longitudinal ones (figs. 
5 2 53> P a S e 96)- At the lower part of the pons, near 
the medulla, the deep set of transverse fibres forms a 
special collection, called 'from its peculiar arrangement, 
the trapezium or corpus trapezoideum (fig. 52, page 96), 
which, as we shall afterwards see, is closely associated 
with the auditory nerve. Traced laterally, all the trans- 
verse fibres of the pons pass into the brachia pontis or 



BRAIN, PONS, WHITE MATTER 99 

middle peduncles of the cerebellum. They are connected 
either with the nucleus pontis of the same side or of 
the opposite side. 

2. Longitudinal Fibres. (i) The SUPERFICIAL 
LONGITUDINAL fibres (fig. 53, page 96) are mostly the 
downward continuation of (a) the anterior pyramids of 
the medulla. In transverse sections they appear as oval 
or rounded bundles behind, the superficial transverse 
fibres, though many of them are intersected by the trans- 
verse fibres (fig. 53, page 96). Behind the pyramids are 
scattered fasciculi, (ft) the cortico-pontine tracts, which 
connect the cerebrum with the nucleus pontis and thence, 
through the middle peduncles, with the cerebellum. 

(2) The DEEP LONGITUDINAL fibres (fig. 53, page 96) 
are placed near the dorsal aspect of the pons, which is 
chiefly made up of the formatio reticularis, and of a 
prolongation of the grey matter of the medulla. The 
following important sets of longitudinal fibres are met 
with in this reticulum : 

(a) The Lemniscus or Fillet, first mentioned on 
page 77, and afterwards on pages 90, consists of four 
chief elements : 

(1) The bulbo-thalamic tract \ 

(2) The spino-thalamic tract / ' 

(3) The lateral fillet. 

(4) Fibres from the nuclei of sensory cranial nerves 

in the medulla and pons. 

(i) Bulbo-thalamic tract. In the medulla this division 
of the fillet, derived, as we have seen, through the 
superior sensory decussation, from the cells of the 
nucleus gracilis and the nucleus cuneatus of the medulla, 
is, at first, represented by delicate arched nerve-fibres, 
which spread out transversely on each side of the mesial 



ioo THE CENTRAL NERVOUS SYSTEM 

raphe". In the lower part of the pons these fibres become 
longitudinal, but are still but a faintly-marked strand. 
At a higher level, however, they form two distinct 
transverse, white bundles, right and left, fusiform in 
transverse section (fig. 53, page 96), which occupy the 
ventral portion of the formatio reticularis, close to the 
middle line, behind the motor pyramidal tracts. They 
constitute the main fillet. 

(2) The Spino-thalamic tract, coming through the in- 
ferior sensory decussation from the cells-of posterior horn, 
unites with the main fillet in the upper part of the pons. 

(3) The Lateral fillet, one of the pathways of the 
sense of hearing, takes its origin from the cells of the 
opposite auditory nucleus. Traced through the striae 
acusticae of the medulla and through the trapezoid body 
of the pons, it forms a distinct bundle which lies on the 
lateral side of the main fillet. At about the middle of 
the pons it diverges from the main fillet, and, as we 
shall see in treating of the crura cerebri, comes to the 
surface at the sulcus lateralis of that division of 
the brain. 

(4) The main fillet is further augmented by fibres 
from the nuclei of sensory cranial nerves, situated in the 
medulla and pons, in each case of the opposite side. 
Thus we see that the fillet is the great crossed sensory 
route to the cerebrum from sensory nuclei in the spinal 
cord, in the medulla, and in the pons. 

(6) The Ascending antero-laterai or Gowers' tract, 
consists, as you know, of three strands, the ventro-spino- 
cerebellar, the spino-thalamic and the spino-tectal. 

(i) The ventro-spino-cerebellar, already noticed in the 
lateral column of the spinal cord (page 24), and in 



BRAIN, PONS, WHITE MATTER 101 

the formatio reticularis of the lateral area of the 
medulla (page 89) ; now ascends in the lateral part 
of the formatio reticularis of the pons. At first it 
consists of scattered bundles, but near the upper border 
of the pons, it forms a distinct, compact strand which 
turns back on itself and descends across the superior 
peduncles of the cerebellum to the cells of the central 
lobe of that division of the brain. 

(2) The spino-thalamic tract was noticed with the 
fillet of which it forms one of the divisions. 

(3) The spino-tectal tract connects the cells of the 
posterior horn with the cells of the tectum of the mid- 
brain (see crura cerebri page 188). 

These several strands are the crossed sensory path- 
ways from the spinal cord to the cerebrum, carrying 
impulses of temperature and of pain, and most of those 
of touch ; the spino-thalamic tract being a direct route, 
the ventro-spino-cerebellar, an indirect one through 
the cerebellum. We have already seen that a few 
of the impulses of common sensibility travel uncrossed 
in the posterior columns of the spinal cord. 

(c) The rubro-spinal or prepyramidal tract is a crossed 
descending tract from the red nucleus in the mid-brain. 
It lies behind the trapezium close to the lateral fillet 
with which its fibres are intermingled. 

(d) The longitudinal bundles anterior and posterior 
already seen in the anterior column of the spinal 
cord and the dorsal aspect of the medulla, lie close to 
each other in the dorsal aspect of the pons near the 
mesial plane (fig. 52, page 96). The former, also called 
tecto-spinal or ventral longitudinal bundle, is connected 
with ocular and pupillar reflexes ; the latter the 
posterior longitudinal bundle by means of collaterals, 



102 THE CENTRAL NERVOUS SYSTEM 

connects and co-ordinates the nuclei of the several motor 
cranial nerves (see page 187). 

(e) The fasciculus teres is the bundle of fibres seen 
near the middle line of the floor of the 4th ventricle. 
It contains fibres of the facial or 7th cranial nerve. 

(/) The olivary fasciculus is found in the formatio 
reticularis dorsal to the mesial fillet. It ends in the 
inferior olive. 

3. Fibres of Cranial Nerves- Transverse sections 
of the pons will further show you the following additional 
fibres : those of the 5th cranial nerve or trifacial with its 
descending root; those of the 6th nerve or abducens ; 
those of the 7th or facial nerve, with the pars intermedia ; 
finally, those of the 8th cranial nerve or auditory (see 
deep origin of cranial nerves, figs 52 and 53, page 96, 
and figs. 82, etc., page 200). 

4. The formatio reticularis is a network of fibres 
which occupies the tegmental part of the pons and is 
continuous with the formatio reticularis of the medulla. 

5. The raphe is a mesial septum which lies behind 
the trapezium, beneath the median groove on the floor 
of the 4th ventricle. It is a continuation of the raphe 
of the medulla, and, like it, is composed of nerve-fibres 
and neuroglia-fibres, which cross each other in every 
direction (fig. 52, page 96). 

2. GREY MATTER OF THE PONS. 

DISSECTION. To see the grey matter of the pons you will require 
a series of transverse sections similar to those represented in plate 
XIV. figs. 52 and 53, page 96. 

The grey matter of the pons consists of multipolar 
and stellate nerve-cells, either scattered or arranged in 
more or less definite groups. Thus we have 



BRAIN, PONS, GREY MATTER 103 

1. The nucleus pontis, situated on the ventral aspect 
of the pons, near the mesial raphe\ amongst the super- 
ficial transverse fibres. It consists of many scattered 
nerve-cells, to which can be traced cortico-pontine fibres 
from the cerebrum ; and ponto-cerebellar fibres to the 
cerebellum. 

2. The superior olivary nucleus (fig. 52, page 96) 
is placed on the dorsal part of the pons, behind the 
trapezium, at some little distance from the middle line, 
in a region which would correspond to the prolongation 
of the lateral area of the medulla. 

3. Substantia gelatinosa Rolando (fig. 52) is con- 
tinuous with that of spinal cord and medulla. 

4. The nuclei of origin of the 5th, 6th, 7th, and 8th 
cranial nerves, for which see 4th ventricle page 124. 

5. The locus eaeruleus is a bluish spot, which will be 
described with the upper part of the floor of the 4th 
ventricle page 122. 

The arterial supply of the pons is derived from the 
basilar artery through the ponticular, posterior cerebral, 
and superior cerebellar branches. 

III. CEREBELLUM. 
(Plates XV. and XVI. Pages 106 and 114.) 

The Cerebellum or Little Brain, the second division 
of the metencephalon, is placed behind the pons and 
medulla, and, like the rest of the brain, is composed of 
grey and white matter. It occupies the two lower fossje 
of the occipital bone, lying beneath the level of the 
tentorium cerebelli, which separates it from the posterior 
part of the cerebral hemispheres. Shaped like an oyster- 
shell, it is ellipsoidal in outline, with its long diameter 



104 THE CENTRAL NERVOUS SYSTEM 

transverse. It consists of a median division, called from 
its worm-like appearance, the VERMIFORM PROCESS or 
vennis cerebelli ; of two lateral divisions, the CERE- 
BELLAR HEMISPHERES; aud of the three PEDUNCLES 
superior, middle, and inferior by means of which it is 
brought into relation with the cerebrum, with the pons, 
with the medulla, and with the spinal cord. 

The median division, the vennis cerebelli or vermiform 
process, though incorporated with the rest of the cere- 
bellum, is a separate division of the little brain. It is 
the only part of the cerebellum which is developed in 
birds, in reptiles, and in fishes. Even in many mammals 
the central lobe is much larger than the lateral lobes. 

We shall consider the several parts of the cerebellum, 
in the following order (i) the hemispheres with (2) their 
lobes and gyri ; (3) the peduncles; (4) the medullary 
vela; (5) the grey matter; and (6) the white matter. 

1. CEREBELLAR HEMISPHERES AND VERMIS 
CEREBELLI. 

(Figs. 55, 56, Plate XV., Page 106). 

The Cerebellar Hemispheres, like those of the cere- 
brum, consist of white matter and of grey matter. 
The white matter forms a central core, the grey matter 
lies mostly on the surface, though minor collections 
occupy the interior. The grey matter of the surface 
cortex cerebelli like that of the cerebrum, though 
darker in colour is thrown into a series of 
delicate, concentric folds, much finer and thinner 
than those of the cerebrum. Moreover, each fold is 
fringed with numberless secondary laminae or leaves, 
giving the characteristic tree-like appearance seen in 
sections of the cerebellum, hence the name arbor vitae. 



BRAIN, CEREBELLUM, HEMISPHERES 105 

Each hemisphere has three surfaces, an upper, a lower, 
and an anterior. 

1. The UPPER SURFACE of each cerebellar hemi- 
sphere is concave and is separated from its fellow, 
along the middle line, by a longitudinal ridge, edged on 
each side, by a shallow groove. This raised portion 
is the upper aspect of the VERMIS CEREBELLI, or 
superior vermiform process (fig. 55, page 106). Across 
it the two cerebellar hemispheres are continuous with 
each other, there being no definite line of demarcation 
between them (fig. 55, page 106). 

2. The UNDER SURFACE of each hemisphere (fig. 56, 
page 106) is, on the other hand, convex, and is divided 
from its fellow by a wide, median, longitudinal hollow, 
the VALLECULA, in which lies the definite, mesial, ven- 
tral division of the cerebellum the VERMIS CEREBELLI 
or inferior vermiform process. Behind, in the middle 
line, the hemispheres are separated by a notch 
INCISURA CEREBELLI POSTERIOR which receives the 
free anterior margin of the falx cerebelli. 

3. The ANTERIOR SURFACE of the cerebellum, narrow 
and convex at the sides, presents, in the middle line, a 
wide cleft the INCISURA CEREBELLI ANTERIOR, which 
lodges the pons and the medulla, and in which, when 
these structures are removed, we see from above 
downwards 

In the middle line, 

(a) the anterior end of the vermis cerebelli ; 

(b) the valve of Vieussens, or superior medullary 

velum ; 

(c) the cavity and roof of the 4th ventricle. 
At the sides are 

(a) the cerebellar hemispheres, with the three 



106 THE CENTRAL NERVOUS SYSTEM 

peduncles superior, middle, and in- 
ferior. 

(6) Across the surface, outside the middle 
peduncle, runs a horizontal sulcus, which 
lodges the flocculus, the inner end of 
which is continuous with the inferior 
medullary velum, a thin white lamina 
extending to the anterior end of the 
vermis cerebelli. This lamina forms part 
of the roof of the 4th ventricle (see fig. 56, 
page 1 06). 

2. LOBES OF THE CEREBELLUM. 

As we have seen, the surfaces of the cerebellar hemi- 
spheres have a laminated appearance, for they are 
broken up by numerous transverse furrows, varying in 
depth, into a series of crescent-shaped folia, with the 
convexities of the crescents directed backwards. These 
folia have been grouped together into lobes, under 
special names, though it must be confessed that the 
lobes, thus formed, are often exceedingly ill-defined. A 
tabular list of them is given on page 107, and they are 
figured on page 106. 

i. On the upper surface of the cerebellar hemispheres 
the lobes, enumerated from before backwards, are as 
follow (fig. 55, page 106) : 

(a) The AL& LOBULI CENTRALIS, situated near 

the centre of the anterior margin, and 
consisting of a few folia, which are con- 
tinuous in the middle line with the central 
lobe of the vermis cerebelli. 

(b) The ANTERIOR SUPERIOR and (f) the POS- 

TERIOR SUPERIOR LOBES. These lobes 



Cerebellum. 

FlG. 55 Upper surface. 



PLATE XV. 



Ala lobi centralis. 
Lobus centralis 



Corpora quadrigemina. 



Incisura cerebclli 
anter. 



crescentic\ 



{cut-men 
clivus 



Commissura 
simplex. 




Horizontal 
fissure. 



CtVpCentic. 



lobus ant. 
-super or 
quadrate. 



Incisura 

cerebelli 

post. 



Lobus 
post, super 

or 
semilunar lobe. 



FlG. 56 



Brachia pontis ~ 



Flocculus. 



Nodulus. 

Tonsilla. 

Biventral 
lobe. 



Lobus yracilis-\-- 



Post, infer. 

or infer, semilunar 

lobe. 




Inferior 

medullary 

velum. 



Furrowed 
band. 

Uvula. 



Pyramid. 



Incisura 
cerebelli 

post. 



Tuber vermis. 



' Lftgui A Cumming. Edinburgh 



> 



BRAIN, CEREBELLUM, LOBES 107 

are separated from each other by a more 
or less distinct sulcus, which arches trans- 
versely across the surface of each hemis 
phere. The anterior superior lobe, often 
called the QUADRATE LOBE, is divided into 
an anterior portion, named the anterior 
crescentic lobus culminis or lobus lunatus 
anterior ; and a posterior portion, the 
posterior crescentic lobus clivi or lobus 
lunatus posterior. The posterior superior 
lobe is also called the superior semilunar 
lobe. Each of the lobes on the upper 
surface is continuous across the vermis 
cerebelli with the corresponding one on 
the opposite side. 

2. On the under surface of the hemispheres, which is 
separated from the upper surface by a horizontal fissure, 
the lobes are better marked, and are more easily dis- 
tinguished from each other (fig. 56, page 106). Enumer- 
ated from behind forwards we find : 

(a) A few folia, the POSTERIOR INFERIOR LOBE; 

or inferior semilunar lobe ; 

(b) The SLENDER LOBE lobu s gracilis ; 
(c} The BIVENTRAL LOBE ; 

(d) The AMYGDALOID LOBE, an oval mass, often 

called the tonsilla ; and, finally, 

(e] The FLOCCULUS, a fringe-like lobe. 

3. On the upper aspect of the vermis cerebelli, enumer- 
ated from before backwards, we find : 

(a) The LINGULA CEREBELLI, consisting of four 

or five folia, which blend with the superior 
medullary velum, 

(b) The LOBULUS CENTRALIS is the small 



io8 THE CENTRAL NERVOUS SYSTEM 

mesially placed lobe lying behind the 
lingula and partly hidden by the next 
lobe. At the Mdes this lobe is prolonged 
on to the hemispheres as two wing-like 
processes, the alae lobi centralis. 
(c} The MONTICULUS CEREBELLI, subdivided 
into culmen monticuli, continuous with the 
lobus culminis of the hemispheres, and the 
clivus monticuli, continuous with the lobus 
clivi of the hemispheres. 

(d) The COMMISSURA SIMPLEX, or folia cacumiiiis. 
4. On the under aspect of the vermis cerebelli the 
lobes are : 

(a) The TUBER VERMIS or TUBER VALVUlwE, 

placed between the posterior inferior and 
the slender lobes of opposite sides (fig. 56, 
page 1 06). 

(b) The PYRAMID, between the biventral lobes. 

(c) The UVULA, between the amygdaloid lobes, 

and connected with them by a grey band, 
called, from its rigid appearance, thefur- 
rowed band (fig. 56, page 106). 

(d) The NODULE or laminated tubercle, the 

pointed anterior end of the inferior vermi- 
form process. It is placed between the 
flocculi, projects into the roof of the 4th 
ventricle, and is continuous with the in- 
ferior medullary velum (page 112). 



As many of the divisions and sub-divisions of the foregoing lobes 
and convolutions are arbitrary, the junior student should content 
himself with observing the facts and not burden his memory with 
the names. 



BRAIN, CEREBELLUM, PEDUNCLES 109 

3 PEDUNCLES OF THE CEREBELLUM. 
(Fig. 44 page 72.) 

The Peduncles of the Cerebellum are bilateral 
bands of white matter, three for each hemisphere. 
They are named the superior, the middle, and the 
inferior peduncles, and they severally connect the 
cerebellum to the pons crura ad pontem ; to the 
medulla crura ad medullam ; and to the cerebrum 
crura ad cerebrum. 

The Superior Peduncles or BRACHIA CONJUNCTIVA 
are two thin, broad, white bands, right and left,' which 
are hidden beneath the anterior part of the cerebellum. 
To see them you will require to divide the cerebellum 
by a vertical median incision, and to draw the parts 
asunder (fig. 44, page 72). They arise in the middle of 
the white substance of the hemispheres, behind the 
inferior cerebellar peduncles. Running upwards, inwards 
and forwards from the anterior aspect of the cerebellum,- 
they reach the dorsal or tegmental part of the cerebral 
peduncles, and are lost beneath four rounded bodies 
called the corpora quadrigemina. By the outer part of 
their under surfaces and by their outer edges, these 
peduncles blend with the pons ; their inner edges, on the 
other hand, are free : their outer edges are, however, 
separated from the pons and the middle peduncles, by a 
groove, which is a prolongation, at an obtuse angle, of 
the sulcus lateralis of the crura cerebri (see page 183). 
At first, the superior peduncles form the lateral walls of 
the upper part of the 4th ventricle, and leave between 
them a triangular interval, which is bridged over by a 
lamina of nerve-substance the VALVE of VlEUSSENS or 
superior medullary velum (fig. 45, page 72). As they ascend 



no THE CENTRAL NERVOUS SYSTEM 

their free edges meet in the middle line, and form part 
of the roof of the 4th ventricle. 

CONSTITUTION The fibres of which the superior 
peduncles are composed come mostly from the corpus 
dentatum, a mass of grey matter in the interior of the 
cerebellum. The majority of the fibres decussate with 
these of the peduncle of the opposite side, and then 
pass up as a distinct bundle, with those that do not 
decussate, and divide into ascending and descending 
branches. The ascending branches go to collections 
of nerve-cells in the higher parts of the brain, the 
descending branches pass down to the pons, to the 
medulla, and to the spinal cord, and become connected 
with the nuclei of the motor cranial and spinal nerves 
in those regions. 

Gowers' tract is also associated with the superior 
cerebellar peduncles, for when it reaches the level of 
the 5th nerve in the pons, it hooks back and follows 
the peduncles to the cerebellum. 

The Middle Peduncles or BRACHIA PONTIS (figs. 
43, 46, page 72 ; fig. 56, page 106) are best seen in front. 
They are the continuation into the cerebellum of the 
lateral part of the pons, that part which lies beyond the 
superficial origins of the fifth cranial nerves. They 
enter the lateral part of the white centre of the 
hemispheres in front of the inferior peduncles, and their 
fibres are so arranged that those which are uppermost 
in the pons radiate to the lowest part of the cerebellar 
cortex, whereas these which are lowest in the pons 
radiate to the highest part of the cerebellum. 

CONSTITUTION All the fibres of the brachia pontis 
become connected with the nucleus pontis. Most of 
them are connected with the nucleus pontis of the 



BRAIN, CEREBELLUM, PEDUNCLES in 

opposite side, a few only with that of the same side. 
Some of the fibres are commissural between the two 
halves of the cerebellum ; others are the continuation 
of the cortico-pontine tracts. 

The Restiform Body or INFERIOR PEDUNCLES 
(figs. 44, 45, page 72) of the cerebellum crura ad 
medullam are two rope-like strands which ascend, 
between the superior and middle peduncles, into 
the white matter of the cerebellar hemispheres. They 
form one of the lateral boundaries of the lower part 
of the fourth ventricle. 

CONSTITUTION (fig. 45, page 72, and fig. 79, page 
1 88). The constitution of the restiform bodies is 
somewhat complex for they consist 

(a) Of fibres from the lateral column of the same 
side through the dorso-spino-cerebellar or lateral 
cerebellar tract already described on page 23 as con- 
necting the posterior spinal nerve-roots, through the 
cells of Clarke's column, with the superior vermis 
cerebelli of the same and opposite sides. 

(b) Of fibres from the nuclei gracilis and cuneatus 
of the medulla of the same side and of the opposite 
side, through the arciform fibres (fig. 79, page 188). 

(c) Of fibres from the olivary nucleus of the opposite 
side (fig. 79, page 188). 

(d) Of fibres uniting the roof nuclei of the cere- 
bellum with the nuclei of origin of the motor cranial 
and spinal nerves. 

Most of the fibres of the restiform body end in the 
cells of the cortex of the superior vermis of the opposite 
side, but they give collaterals to the vermis of the same 
side. 



ii2 THE CENTRAL NERVOUS SYSTEM 

4. MEDULLARY VELA. 

r. The Superior Medullary Velum VALVE of 

VlEUSSENS (tig. 45, page 72) is a delicate sheet of 
nerve-substance placed across the triangular interval 
left between the two superior cerebellar peduncles 
before they meet in the middle line. Triangular in 
shape, with its apex forwards, it forms part of the 
roof of the upper division of the 4th ventricle. It 
consists of a white lamina, crossed on its upper surface 
by several transverse grey ridges, with intervening 
furrows called the LINGULA CEREBELLI (fig. 45, page 
72). The white and grey matter of the valve of 
Vieussens are continuous at the sides with the white 
and grey matter of the cerebellar hemispheres. 

2. The Inferior Medullary Vela valves of Tarini 
consist of two thin, delicate, white, semilunar 
sheets of nerve-substance, like little swallows' nests, 
one on each side, hidden beneath the amygdaloid 
lobes of the cerebellum, which must be removed with 
great care to see them. The inferior convex borders 
of each of these semilunar folds blends with the white 
substance of the inferior vermiform process and with a 
band called the furrowed band ; their anterior concave 
semilunar edges are free, or rather, are continuous with 
the layer of epithelium which lines the under surface 
of the pia mater roofing over the 4th ventricle. 
Externally these two senilunar folds are attached by 
a white band or peduncle to the flocculus ; internally, 
a central, very thin portion, continues the lateral 
portions across the middle line in front of the nodule 
(fig. 56, page 1 06). 



BRAIN, CEREBELLUM, GREY MATTER 113 

5. GREY MATTER OF THE CEREBELLUM. 
(Figs. 55, 56, Page 106). 

The Grey Matter of the cerebellum consists of 
two parts : that on the surface the cortex cerebelli 
or cortical ganglia ; that in its interior the nuclei 
cerebelli, or subcortical ganglia. 

1 . CORTEX CEREBELLI The grey matter of the cortex 
of the cerebellum not only covers its surface, but lines 
the sides and passes across the bottom of its various 
fissures or sulci, so that in reality it forms a thin 
lamina or cloth folded on itself in a series of delicate 
leaves or plates. A mesial vertical section will enable 
you to see this arrangement, and will show you the 
beautiful tree-like appearance ARBOR VITVE of the 
grey and white matter (fig. 58, page 114). 

2. NUCLEI CEREBELLI. The chief masses of grey 
matter in the interior of the cerebellum are the 
CORPORA DENTATA, placed one in each hemisphere 
(fig. 58, page 1 14). In structure they are similar 
to the corpora dentata of the olivary bodies, and 
are, as you will remember, closely connected with 
them. They each consist of a wavy band of brown- 
coloured nerve-substance, enclosing white matter, the 
whole forming an oval, pouch-like, wavy capsule, open 
at its upper and inner side (fig. 58, page 114). Through 
this opening bundles of white nerve-fibres enter or 
leave the centre of the corpus dentatum. They can be 
traced from the brachia conjunctiva, from the superior 
medullary velum, and from the restiform body. 

The other nuclei are found in the central lobe of the 
cerebellum. They are the nucleus globosus, the nucleus 
emboliformis, and the nucleus tecti or fastigii and are 

i 



ii4 THE CENTRAL NERVOUS SYSTEM 

situated near the middle line, internal to the corpora 
dentata. 

MINUTE STRUCTURE OF THE GREY MATTER. 

The grey cortex of the cerebellum consists of three 
layers (fig. 57, page 114) 

(1) An outer the molecular layer. 

(2) A middle the layer of Purkinje's cells. 

(3) An inner the granular layer. 

1. The OUTER LAYER molecular layer forms a 
clear, grey coloured stratum on the surface of the 
cerebellum. It is composed of a delicate matrix of 
neuroglia, of fine nerve- fibres, and of nerve-cells and 
their processes. The nerve-cells are of two kinds (fig. 
57, page 114). 

(1) Small molecular cells, mostly situated in the 
outer part of the layer, are multipolar cells with 
many protoplasmic processes and with an axis- 
cylinder process which ramifies in this layer. 

(2) Large molecular cells placed at the deeper 
part of the molecular layer are transversely elongated, 
and have 

(a) Protoplasmic processes, which ramify towards 
the surface of the cortex ; and 

(b] An axis-cylinder process, which runs trans- 
versely between the molecular and granular layers, and 
which gives off, at right angles to its direction, 
branches whose terminal twigs envelop the bodies of 
the cells of Purkinje, seen in the next layer, in a 
basket-like network ; hence they are called basket cells 
(fig. 57, page 114). 

2. The MIDDLE LAYER is formed of cells which are 
characteristic of the grey matter of the cerebellum. 



FIG. 57. 
Cerebellum Structure. 



Large granular 
cell. 




Protoplasmic, 
process. 



PLATE XVI. 



Middle layer 

or layer of 
Purkinje's cells 



Small 
granular 
cell. 

Axone of 
Purkinje's cell. 



-Moss fibres. 

Axone of 
ge molecular cell. 



Molecula 
layer. 



Granular 
layer. 



FIG. 59. 



FIG. 58. 



( externa 
Corpora \ 

genuulata } 

I interna 




Pons. 

Corpus 
dentatum. 



Corpus 
callosum. 

Olfactory 
area of Broca. 

Locus 
foratus 
anticus. 

, . Corpora 
Miammillaria. 



Medulla. 



Corpora? Pulvinar. 

quadrigemina . 



BRAIN, CEREBELLUM, STRUCTURE 115 

They are called the CELLS of PURKINJE (fig. 57, page 
1 14), or from their shape ANTLER CELLS. They are 
large, flask-shaped cells, set at right angles to the 
surface of the cerebellum. Their larger ends are the 
deeper, and give off a single slender process the axis- 
cylinder process which, after becoming medullated, 
sends off lateral branches, and then enters the central 
core of white matter. Of the lateral branches some pass 
into the molecular layer, some spread out in the granular 
layer. The outer process of the cells is much thicker 
and larger, and breaks up into leaf-like branches, like 
the horns of a deer, hence the name antler cells. These 
branches, called dendrones or protoplasmic processes 
spread out, like an espalier, in planes across the laminae, so 
that they present different appearances according to the 
plane of the section (fig. 57, a, b, page 114). Ultimately 
they form a rich plexus, ramifying towards the surface. 
These ramifications end free, and most likely do not 
anastomose with each other, nor with -the processes of 
neighbouring cells, though some of them are said to 
be attached to the connective tissue, and to the blood- 
vessels, at the margin of the molecular layer. Both 
the base and the branches of the peripheral dendrones 
of Purkinje's cells are beset with a network of fine 
fibrillae called neuro-fibrillae. 

3. The INNER or GRANULAR LAYER rust-coloured 
layer consists of nerve-cells and of neuroglia-cells 
embedded in a delicate matrix of fine interlacing 
fibrillae. 

Its nerve-cells are of two kinds small granular 
and large granular (fig. 57. page 114). 

(i) The small granular cells are polyhedral in shape. 
Their protoplasmic processes end in little tufts of short 



n6 THE CENTRAL NERVOUS SYSTEM 

thick branches (fig. 57, page 114). Their axis-cylinder 
process is very slender, and arises either from the 
body of the cell or from one of the protoplasmic 
processes. Passing with an undulating course towards 
the molecular layer, the axis-cylinder process ends 
in two branches which run parallel with the laminae 
of the cerebellum. 

(2) The second kind of cells the large granular 
cells, though scattered throughout the thickness of the 
granular layer, are mostly found in its outer part. 
They are stellate in shape and have axis-cylinder and 
protoplasmic processes, the former giving off numerous 
collaterals (fig. 57, page 114). 

Note that the whole of the cerebellar cortex, so 
unlike that of the cerebrum, has one and the same 
structure throughout, the cells of Purkinje being its 
main feature. We can therefore conclude that, most 
likely, all parts, of the cerebellar cortex have the same 
function. Special areas, however, are supposed to 
preside over special groups of muscles. 

6. WHITE MATTER OF THE CEREBELLUM. 
(Fig. 57, Plate XVI. Page 114). 

The White Matter of the cerebellum consists of 
three sets of fibres (i) projection, (2) association, 
(3) commissural. 

(1) The projection fibres are those which, leaving 
their own segment of the central nervous system, travel 
to higher or lower segments of the same system. They 
may be .crossed or uncrossed. 

(2) The commissural fibres unite corresponding 
areas of their own segment across the middle line. 

(3) The association fibres are confined to their own 



BRAIN, CEREBELLUM, WHITE MATTER 117 

segment and to the same side of that segment. They 
unite groups of nerve-cells of the same side. 

These three sets of fibres constitute the entire white 
core of the cerebellum. 

We shall consider (i) their structure, (2) then their 
arrangement. 

1. STRUCTURE. The fibres of the cerebellum are 
either 

(1) the axis-cylinder processes of the cells of 
Purkinje already described on page 1 15, or they are 

(2) fibres which, on reaching the grey matter, 
divide frequently, and at this point, or at some other 
part of their course, form little mossy tufts of short 
thick branches hence they are called moss -fibres 

(fig- 57. P a g e * '4) ; or tne >' are 

(3) a set of fibres climbing or tendril -fibres, 
which end in a plexus in the molecular layer, and 
appear to be prolongations of Purkinje's cells, though 
not so in reality, for they merely form a network 
round the attached ends and processes of the dendrones, 
of the cells of Purkinje (fig. 57, page 1 14). 

2. ARRANGEMENT of the nerve-fibres of the cere- 
bellum 

The association fibres connect, as we have seen, the 
cells of one convolution with those of another con- 
volution of the same side. 

The commissural bands unite the cerebellar hemi- 
spheres across the middle line They will be found near 
the anterior and posterior ends of the vermis cerebelli. 

The projection fibres form the chief part of the 
cerebellar peduncles. They are divided into two sets ; 
these going to the cerebellum or centripital ; and these 
leaving the cerebellum or centrifugal. 



n8 



THE CENTRAL NERVOUS SYSTEM 



(a) The centripital fibres all end in the cells of 
Purkinje of the cortex cerebelli. 

The following are the chief groups :- 



Those from 

the Spinal 

Cord. 



Those from 
the Medulla. 



Those from 
Cerebrum 
and Pons. 



1. The ventro-spino-cerebellar, Cowers'") Through 

tract, from Clarke's column of the I the 
opposite side to the cortex of the j superior 
central lobe of the cerebellum. J peduncles. 

2. The dorso-spino-cerebellar tract from" 

the cells of Clarke's column of the 
same side to the cerebellar cortex of 
the lateral lobe of that same side. 

3. Arcuate fibres, 

(a) from the nuclei gracilis and 
cuneatus of the medulla of the same 



and opposite sides to the cortex of 
the lateral lobe of their own side. 

(/;) from the cells of the opposite 
inferior olives to the cortex of the 
lateral lobe. 

Cortico-pontine tracts, from the cerebral" 
cortex (frontal, parietal and temporal 
lobes) to the nucleus pontis of the 
same side, thence by new relays, 
through the middle peduncles, to the 
opposite cerebellar cortex. 

Fibres from the lateral vestibular 
nucleus of Deiters to the vermis 
cerebelli of the same side. 



Through 

the 
inferior 



peduncles. 



Through 

the 

middle 
peduncles. 



(b} The centrifugal fibres come from the cerebellar 
subcortical ganglia, chiefly from the corpus dentatum. 
They consist of the following sets : 

(1) Fibres from the corpus dentatum through the 
superior peduncles to the opposite red nucleus, thence 
by the new relays of fibres to the cerebral cortex. 

(2) Fibres which course from the corpus dentatum 
through the middle peduncles to the opposite pontine 



BRAIN, FOURTH VENTRICLE 119 

nucleus, thence through the crura cerebri to the 
cerebral cortex. 

(3) Fibres, crossed and uncrossed, from the roof 
nuclei to the vestibular nucleus, to nucleus of Deiters, 
and to the nuclei of other sensory nerves in the medulla. 

The FUNCTIONS of the cerebellum are as yet un- 
known, but experiments point to the fact that it is a 
reflex centre for the co-ordination of muscular move- 
ments, such as walking. Some hold that it is a centre 
which presides over equilibrium. The cerebellum may, 
however, also contain psychical centres like the cerebrum. 

THE 4TH VENTRICLE. 
(Fig. 44, Page 72, and Fig. 50, Page 90). 

DISSECTION. To expose the 4th ventricle make a sagittal 
section through the back of the cerebellum and gently draw the 
parts asunder. This will expose the back of the medulla and pons. 

ITS POSITION, FLOOR, ROOF, WALLS, AND NUCLEI. 

In describing the posterior aspect of the medulla 
oblongata, on page 75, you will remember we treated 
of its lower or posterior division only ; we now pro- 
ceed to consider its anterior or upper division that 
half which is connected with the 4th ventricle. 

The 4th Ventricle is a conical-shaped space with 
its apex backwards. It is placed between the medulla 
and pons in front and the cerebellum behind. Lodged in 
the fore part of the vallecula on the under surface of the 
cerebellum, it has a quadrilateral floor and a tent-like 
roof. We shall require to examine (i) its floor, (2) its 
lateral boundaries, (3) its roof, (4) its lining, ($) the 
openings into it, (6) its blood vessels or choroid plexus, 
(7) the various collections of grey matter or nuclei 



120 THE CENTRAL NERVOUS SYSTEM 

beneath the floor, and lastly, (8) its strands of nerve- 
fibres. 

I. The Floor, or Anterior Wall of the 4th 
Ventricle (fig. 44, page 72), is a diamond-shaped 
depression, of the figure of an heraldic lozenge, and 
resembles two triangles placed base to base. It looks 
backwards and upwards, and its lower or posterior 
half occupies the back of the medulla ; its upper or 
anterior half the back of the pons. Its formation is 
due to the separation from each other of the walls of 
the posterior median fissure of the spinal cord, and 
the consequent opening out ot the central canal of the 
cord, thus bringing the grey matter round that canal 
nearer to the surface. Of its four angles, two are lateral 
right and left and mark the widest transverse 
diameter of the ventricular floor ; of the other two 
angles, the superior is on a level with the upper 
border of the pons, the inferior on a level with the 
lower border of the olivary body. From some 
supposed likeness to a writing pen, the apex of the 
lower part of the ventricular floor has been called the 
calamus scriptorius. At the lateral angles the space is 
prolonged for a short distance between the cerebellum 
and medulla, the prolongations being called lateral 
recesses. Running across the widest part of the 
ventricular floor, opposite the lateral angles, are the 
stria medullares or striae acusticce (fig. 44, page 72), 
which join the auditory nerve, and which, you will 
remember, mark the upper limit of the medulla on 
this aspect. They also serve to divide the ventricular 
floor into two divisions, a lower portion belonging to 
the medulla, and an upper portion belonging to the 
pons (fig. 44 page 72), both of which are again sub- 



BRAIN, FOURTH VENTRICLE 121 

divided, by the vertical median groove that runs from 
the superior to the inferior angle, into two lateral 
segments. Thus we get the entire ventricular floor 
mapped out into four divisions two above and two 
below the striae medullares (fig. 44 page 72). On 
examining each of the lower divisions you will see, at 
about their centre, a small triangular depression called 
the INFERIOR or POSTERIOR FOVEA (fig. 44, page 72), 
the base of which is directed downwards, the apex 
upwards, in close contact with the striae ; while its 
inner and outer margins are prolonged downwards as 
two grooves, the inner one until it meets the central 
median furrow near the lower angle of the ventricle, 
and the outer one until it reaches the lateral wall of the 
cavity. Thus we find that each part of the lower 
division of the ventricular floor can be mapped out into 
the following four distinct areas : 

1. The inferior fovea (fig. 44, page 72), the space 
enclosed within the sides of the triangular depression 
just described. 

2. A raised area, which lies between the median 
furrow and the inner margin of the fovea. It forms 
the lower part of the fasciculus or eminentia teres, 
and is often called the trigonum hypoglossi (fig. 44, 
page 72). 

3. The trigonum acusticum, with the tuberculuni 
acusticum, is enclosed between the lateral wall and the 
outer margin of the fovea (fig. 44, page 72). It is a part 
of a larger area, area acustica, situated above the striae 
medullares which cross it superficially. 

4. The ala cinerea -- trigonum vagi, with the 
eminentia cinerea, is placed below the base of the 
inferior fovea (fig. 44, page 72). 



122 THE CENTRAL NERVOUS SYSTEM 

In like manner each of the two upper segments of 
the ventricular floor, which differ from those of the 
lower half in being covered by a thin layer of white 
matter, has a similar triangular depression (fig. 44, 
page 72), the SUPERIOR or ANTERIOR FOVEA between 
which and the central furrow is (i) the eminentia teres, a 
prolongation of \\\t fasciculus teres. Extending from the 
apex of this fovea to the upper angle of the ventricle is a 
shallow depression, which, from its dark aspect, is called 
(2) the locus caruleus (fig. 44, page 72 ; fig. 50, page 90), 
the colour being due to a mass of pigmented nerve-cells 
substantia ferruginea lying beneath. 

II. The Lateral Walls of the 4th Ventricle. 
The lateral boundaries of the lower half of the 
ventricular cavity are formed from below upwards by 
(l) the FASCICULUS GRACILIS and its CLAVA fig. 44, 
page 72) ; (2) higher up, by the tapering end of the 
FASCICULUS CUNEATUS (fig. 44, page 72); and (3) highest 
of all by the RESTIFORM BODY or inferior peduncle 
of the cerebellum (fig 44, page 72). The boundaries 
of the upper division of the floor are the SUPERIOR 
CEREBELLAR PEDUNCLES or brachia conjunctiva (fig 44, 
page 72) of the two sides. 

III. The Roof of the 4th Ventricle is tent-like 
in shape its apex projecting backwards towards the 
cerebellum. The lower half of the roof is formed by 
pia mater, which at this point is reflected from the 
cerebellum to the back of the medulla. It is, however, 
deficient in the middle line, a hole, called the foramen 
of Majendie, being left in the roof. Its under surface 
is lined by a layer of flattened epithelial cells, and a 
thickening ol this epithelium at the lower angle of the 
ventricle is called the obex (fig. 44, page 72). A 



BRAIN, FOURTH VENTRICLE 123 

similar thickening, with the addition of a little white 
nervous matter, skirting the side of the lower half of 
the floor, is called the ligula or tcenia (fig. 44, page 72). 
The roof of the upper portion of the ventricle is formed 
partly by the SUPERIOR CEREBELLAR PEDUNCLES 
brachia conjunctiva after they meet in the middle 
line, and partly by the SUPERIOR and INFERIOR 
MEDULLARY VELA, laminae of grey and white matter 
already described on (page 112). 

IV. Ependyma Ventrieulorum. The floor of the 
4th ventricle is covered by a layer of grey matter 
the ependyma ventriculorum, consisting of neuroglia 
derived from the central grey nucleus round the canal 
of the spinal cord. Upon this ependyma lies a layer 
of ciliated epithelial cells continuous with the epith- 
elium which lines the central canal of the spinal marrow, 
and the cavities of the third and lateral ventricles 
inside the cerebrum. 

V. Opening's into the 4th Ventricle. At its 
upper angle, the 4th ventricle communicates by a 
narrow channel, AQUjEDUCTUS CEREBRI aqueduct of 
Sylvius, with the THIRD VENTRICLE (fig. 67, page 152) ; 
below, at the inferior angle, the cavity is continuous 
with the CENTRAL CANAL of the SPINAL CORD ; behind, 
at the lower part of the roof, just above the inferior 
angle, a small rounded opening in the pia mater, the 
FORAMEN of MAJENDIE, puts the ventricle in communica- 
tion with the SUB-ARACHNOID SPACE ; while at each side, 
near the lateral angles, are similar openings in the 
roof, between the cerebellum and medulla. Through 
these openings the cerebro-spinal fluid can find its 
way from the sub-arachnoid space into the cavities of 
the brain and spinal cord. 



i2 4 THE CENTRAL NERVOUS SYSTEM 

VI. Choroid Plexus. The choroid plexus of the 
4th ventricle consists of two longitudinal, vascular folds 
of the pia mater which forms the roof of the 4th 
ventricle. These vascular fringes run along each side 
of the middle line of the roof, projecting towards the 
ventricle, though covered everywhere by the epithelium 
which follows all their windings and folds, and thus 
separates them from the cavity of the ventricle. Part 
of this plexus projects, as a vascular tuft, into each 
lateral recess. 

VII. Grey Matter beneath the Floor of the 4th 
Ventricle. Connected with the grey matter of the 
floor of the 4th ventricle we have the nuclei of origin 
of most of the cranial nerves. 

(a) Nuclei beneath the lower division of the ven- 
tricular floor (fig. 44, page 72, and fig. 50, page 90): 

(1) The first of these nerve-nuclei lies beneath the 
lower part of the surface prominence known as the 
eminentia or fasciculus teres, which skirts the median 
furrow on the ventricular floor. This prominence not 
only occupies the lower part of this area, but also 
passes up under the striae medullares to the upper 
part of the floor of the ventricle. In its lower 
part it covers the NUCLEUS of the HYPOGLOSSAL or 
1 2th nerve, and hence is often called the trigonum 
hypoglossi ; and, in transverse sections of the medulla 
at this level, the fibres of the I2th nerve may be seen 
running outwards and forwards from the nucleus beneath 
this area towards the periphery (fig. 49, page 84). 

(2) The trigonum acusticum or trigonum vestibulare 
or area vestibularis and its tubercle correspond in 
position to the tubercle of Rolando, and cover the 
AUDITORY NUCLEI. This trigone lies at the lateral 



BRAIN, FOURTH VENTRICLE 125 

angle of the ventricle, close to the striae acusticae, but 
also extends beneath the striae into the upper division 
of the ventricular floor (fig. 50, page 90). 

(3) The ala cinerea and the eminentia cinerea contain 
the nuclei of origin of several nerves ; thus in its lower 
part, we have the medullary part of the nucleus of the 
SPINAL ACCESSORY NERVE (fig, 50, page 90) ; in its 
upper part, and extending into the inferior fovea, are 
the nuclei of the VAGUS below and of the GLOSSO- 
PHARYNGEAL above (fig. 50, page 90). 

(b] The nuclei beneath the upper division of the 
ventricular floor, viz. that formed by the back of the 
pons, are the following : 

(1) Close to the lateral recesses are the SENSORY 
and MOTOR nuclei of the 5th nerve, the motor being 
internal, the sensory external (fig. 50, page 90) ; 

(2) The NUCLEUS of the 6th nerve lies under the 
fore part of the fasciculus teres ; superficial to, but 
higher up and nearer the middle line than the nucleus 
of the /th (fig. 50 page 90). 

(3) The NUCLEUS of the /th or facial nerve is 
placed deeper, and internal to the nucleus of the 5th, 
but external to the nucleus of the 6th nerve (fig. 50, 
page 90). 

(4) The outer or ACCESSORY NUCLEUS of the auditory 
or 8th nerve lies external to the facial nucleus. 

These various nuclei will be again referred to in 
the section on the Superficial and Deep Origins of the 
Cranial Nerves, page 197. 

VIII. The White Matter of this part of the 
medulla, as we have seen, consists of the continuation 
of the pyramids, and behind these, of the formatio 
reticularis, and of the three important longitudinal 



126 

strands the fillet, and the anterior and the posterior 
longitudinal bundles. The former, the fillet, is derived 
from the posterior columns, being in part a continuation 
of the sensory decussation ; the latter the longitudinal 
bundles, are connected with the antero-lateral columns 
of the spinal cord, and can be traced up under the 
grey matter of the floor of the 4th ventricle to the 
crura cerebri. 

IV. THE CEREBRUM 

GENERAL OUTLINE. The cerebrum is by far the 
largest division of the brain, and on an average, 
weighs about 30 oz. Above, it occupies the vault 
of the cranium ; below, at its base, it is lodged, 
in front within the anterior and middle cranial fossae, 
but behind, it rests on the upper surface of the ten- 
torium cerebelli. An egg-shaped mass of nervous 
substance, it is larger behind than in front, and is partly 
separated by the great longitudinal fissure into two 
halves the CEREBRAL HEMISPHERES which are united 
across the middle line by a thick band of white matter, 
the great cerebral commissure, the CORPUS CALLOSUM. 
Each hemisphere is ovoid in shape, and is composed 
of a white stalk or peduncle the PEDUNCULI or CRURA 
CEREBRI surmounted by a convoluted grey crust or 
cortex, mapped out, in the greater part of its extent, by 
furrows or SULCI into a series of larger or smaller 
folds called convolutions or GYRI. 

Internally the cerebrum consists of collections of 
grey matter called SUBCORTICAL GANGLIA, in contra- 
distinction to the cortical ganglia on the surface; (2) 
of strands of white nerve-fibres, PROJECTION, ASSOCIA- 
TION and COMMISSURAL FIBRES; and (3) of a large 



BRAIN, CEREBRUM EXTERIOR 127 

central cavity, subdivided into smaller spaces, called 
VENTRICLES. 

We shall describe (i) the EXTERIOR or cortex of 
the cerebrum with its FISSURE, LOBES, and GYRI ; (2) 
the BASE; (3) the INTERIOR, with its VENTRICLES, its 

GANGLIA, its COMMISSURES and Other WHITE STRANDS; 
and, finally, (4) the CEREBRAL PEDUNCLES or crura 
cerebri. 

I. EXTERIOR OF THE CEREBRUM. 
(Figs. 60, etc., Plates XVII. and XVIII Page 130). 

The Grey Matter of the outer surface of the 
cerebrum is known as the great hemispherical 
ganglion, the CORTEX or the bark of the brain. It 
consists of a frilled or crumpled cloth or mantle of grey 
matter about ^ in. in thickness, the frills being the 
convolutions, the intervals between the frills being the 
fissures. It is divisible into a larger, upper part, called 
the pallium ; and a smaller, basal part, called the olfac- 
tory brain or rhinencephalon (see page 141). 

Each hemisphere is a triangular pyramid, and 
has three borders separating three surfaces an outer 
or lateral surface, convex ; and inner or mesial, plane 
and vertical , and an irregular under-surface or base. 
Examine (i) the fissures and sulci : (2) the lobes and 
gyri of these surfaces. 

1. FISSURES OF CEREBRAL HEMISPHERES. 
(Figs.6o,6i, Plate XVII. Page 130; Figs. 62,63, Plate XVI 1 1. Page 130). 

Of the Fissures and Sulci of the hemispheres the 
largest and most evident subdivide the surface of 
the cerebrum into lobes, and may be called INTEK- 
LOBULAR ; the smaller fissures INTRA-LOBULAR 



128 THE CENTRAL NERVOUS SYSTEM 

divide the lobes into convolutions or gyri, which, in 
most cases, have received definite designations. 

Note. The term fissura is often used to indicate those clefts 
only which cause corresponding elevations in the interior of 
the cerebrum the remaining clefts being called sulci. In this 
volume the clefts which break up the cerebrum into lobes are called 
fissures : these which subdivide the lobes are called sulci. 

i. The Inter- lobular Fissures are the FISSURE 
OF SYLVIUS or fissura cerebri lateralis ; the FISSURE OF 
ROLANDO or fissura cerebri centralis ; and the PARIETO- 
OCCIPITAL FISSURE (figs. 60, 6 1, page 130). 

(1) The Fissure of Sylvius or FISSURA CEREBRI 
LATERALIS, unlike the other fissures of the hemi- 
spheres, is not a mere indentation of the cerebral cortex, 
but is formed by the folding upon itself of the entire 
cerebral substance. It is a deep cleft with the mouth 
of the cleft in front. Beginning near the middle line 
on the under surface of the hemisphere at a point called 
the anterior perforated spot, it runs transversely 
upwards and outwards to the lateral aspect of the 
hemisphere and there divides into two limbs an 
anterior short, vertical, ascending limb, and a posterior 
horizontal limb which runs backwards and upwards on 
the outer surface of the hemisphere. Sometimes there 
are two short limbs the one being called anterior, 
the other vertical (fig. 60 page 1 30). 

(2) The Fissure of Rolando or FISSURA CEREBRI 
CENTRALIS (figs. 60, 6 1, ~ page 130), is one of the first 
fissures to appear in the development of the brain. 
It commences above at or close to the median longi- 
tudinal cleft, and in some cases even appears on the 
inner surface of the hemisphere. Descending obliquely 
forwards across the outer surface of the cerebrum, it 



BRAIN, CEREBRUM, FISSURES 



129 



ends below near the anterior part of the horizontal 
limb of the fissure of Sylvius, but in most cases falls 
somewhat short of that fissure. It is not of uniform 
depth throughout, being deeper below than above. 

(3) The Parieto occipital Fissure (figs. 61, 62, page 
130), appears on both the outer and inner surfaces of 
the hemisphere. The external portion of this fissure 
is a short cleft on the outer aspect of the hemisphere 
near its hinder end. It is called the EXTERNAL PARIETO- 
OCCIPITAL FISSURE. The mesial part of this same 
fissure INTERNAL PARIE-TO-OCCIPITAL FISSURE is 
continuous above with the external part, and is a well- 
marked and very constant cleft, which descends 
vertically on the mesial aspect of the hemisphere. It 
will be noticed with that surface (fig. 61, page 130). 

2. The Intra-lobular clefts or Sulci separate indi- 
vidual convolutions from each other, and will be 
described with the convolutions which they serve to 
map out. Those which have received special names 
are 



1. Praecentral sulcus. 

2. Postcentral sulcus. 

3. Intra-parietal sulcus. 

4. Superior temporal, or 

parallel sulcus. 

5. Sulcus orbitalis or triradiate. 

6. Collateral sulcus. 



7. Sulcus corporis callosi or 
callosal sulcus. 

8. Calloso-marginal or sulcus 
cinguli. 

9. Sulcus calcarinus or cal- 
carine sulcus. 

10. Hippocampal or dentate 
sulcus. 

These sulci are figured in figs. 60, 61, page 130; figs. 
62, 63, page 1 30. 



130 THE CENTRAL NERVOUS SYSTEM 

2. LOBES AND CONVOLUTIONS OF CEREBRAL 
HEMISPHERES. 

I. Lobes and Gyri of the Lateral Surface. The 

cerebral hemispheres are, in the early stages of their 
development, perfectly smooth and without con- 
volutions. This developmental type is retained in the 
case of many animals, e.g. in the insectivora. In the 
adult brain each cerebral hemisphere has five principal 
lobes. Of these, four are bounded by the inter-lobular 
fissures, and take their names from the bones of the 
skull in relation to which they lie : they are the frontal, 
the parietal, the occipital, and the temporal lobes. The 
fifth lobe the central lobe, insula, or isle of Reil is 
not in contact with the bones of the skull, but is 
hidden within the fissure of Sylvius, the margins of 
which must be separated in order to see it. Two 
other lobes are sometimes described the olfactory lobe 
and the limbic lobe, which, together, form the olfactory 
brain (see page 141). 

(i) The Frontal Lobe (fig. 60, 61, page 130) is 
pyramidal in shape, its rounded anterior end being 
called the frontal pole. It has three surfaces an outer 
or lateral, an inner or mesial, and an inferior or orbital. 

The outer surface is bounded behind by the FISSURE 
OF ROLANDO or fissura cerebri centralis, which separates 
it from the parietal lobe ; below, by the FISSURE 
OF SYLVIUS or fissura cerebri lateralis, which separates 
it from the temporal lobe ; internally by the GREAT 
LONGITUDINAL FISSURE, which separates it from its 
fellow of the opposite side. It has four gyri ; one, 
the ASCENDING FRONTAL CONVOLUTION or anterior 
central gyrus (figs. 60, 6 1, page 130), runs parallel with, 
and anterior to the fissure of Rolando. In front, it is 



<S. cinguli. 



FIG. 62. 

8. corporis callosi. 

~ 



G. subcallosus. 



I. Centre for smell. 

II. ,, taste. 

III. sigkt. 

IV. , motion. 



PLATE XVIII. 



^<S. sub^parietalis. 
Int. parieto-ocript. 




. 
hippocampi. 

fiss. calcarina. 



Fiss. collaterals. 



Olfactory area 
of Broca. 



FIG. 63. 



S.orbttaKsor 
triradiatefias. 



Anterior perforated 
space. 



Collateral 
fissure. 



I 

Infer, temporal ' 
fissure. 



Gyrus rectus. 



.Orbital surface 
of frontal lobe. 



Inxida. 
Operculum. 




Under surface 

of temporal and 

occipital lobe. 



Convolutions of Inner and Under Surface of Cerebrum. 



BRAIN, CEREBRUM, CONVOLUTIONS 131 

limited by the praecentral sulcus (fig. 60, page 130), 
behind by the fissure of Rolando. The rest of the surface 
in front of this gyrus is mapped out by two horizontal 
parallel sulci the superior and inferior frontal sulci 
into three antero-posterior convolutions the SUPERIOR, 
the MIDDLE, and the INFERIOR FRONTAL GYRI, which 
are sometimes classed together under the term pre- 
frontal lobe (fig. 60, 61, page 130). The posterior part 
of the left inferior frontal gyrus is called Broca's 
convolution. It deserves special notice, for it is 
supposed to contain the motor centre for speech, but 
doubt has, with much justice, been thrown on this state- 
ment, for there are cases recorded in which destruction 
of this centre has been unaccompanied by aphasia or 
loss of speech. It curves round the anterior and 
vertical limbs of the fissure of Sylvius, by which means 
it can be subdivided into three parts an anterior part, 
pars orbitalis ; a middle part, pars triangular is ; and a 
posterior part, pars opercularis (fig. 60, a, b, c, page 1 30). 
The orbital or under surface of the frontal lobe, 
bounded, on' the inner side by, the longitudinal fissure 
and behind, by the fissure of Sylvius, becomes continuous 
in the rest of its extent with the outer aspect of the 
hemisphere. At about its centre it has a three-legged 
or H shaped sulcus the triradiate or sulcus orbitalis 
which subdivides the surface into three gyri, an 
INTERNAL ORBITAL, an ANTERIOR ORBITAL, and a 
POSTERIOR ORBITAL (fig. 63, page 1 30). These are each 
mere prolongations into this surface, though not directly, 
of the convolutions of the outer surface. Thus the 
superior frontal gyrus becomes continuous with the 
internal orbital, the middle with the anterior orbital, 
and the inferior with the posterior orbital. 



1 32 THE CENTRAL NERVOUS SYSTEM 

On the surface of the internal orbital gyrus, lodged in 
a triangular sulcus the OLFACTORY GROOVE is a club- 
shaped body, the OLFACTORY BULB and its PEDUNCLE, 
which are sometimes regarded as a separate lobe (see 
page 141). The portion of the internal orbital con- 
volution internal to the olfactory groove is called the 
gyrus rectus. It is separated behind by a slight sulcus 
from an area which is called the area of Broca. 
(fig. 62, page 130, and fig. 59, page 114). 

The inner or mesial surface of the frontal lobe will 
be described with the corresponding surface of the 
hemisphere, page 137). 

TABLE OF THE FRONTAL GYRI. 

Gyrus centralis anterior or 

ascending frontal. 

Outer surface ^ Gyrus frontalis superior. 
Gyrus frontalis medius. 
Gyrus frontalis inferior. 

Frontal lobe Inner surface j See mesial surface of hemi- 

( spheres. 

i Internal orbital. 
Anterior orbital. 
Posterior orbital. 

(2) The Parietal Lobe has an inner surface, which is 
flat and vertical, and belongs to the inner aspect of the 
hemisphere (see mesial surface, page 137); and an outer 
surface, lateral and convex, which is bounded in front 
by the fissure of Rolando, separating it from the frontal 
lobe ; behind by the external parieto-occipital fissure, 
separating it from the occipital lobe, and below by 
the fissure of Sylvius and its projection backwards, 
separating it from the temporal lobe. 



BRAIN, CEREBRUM, CONVOLUTIONS 133 

This surface is furrowed by two sulci the one is 
directed downwards parallel to and behind the fissure 
of Rolando, and forms the posterior limit of the 
ASCKNDING PARIETAL CONVOLUTION or gyrus centralis 
posterior ; the other, the intra-parietal sulcus, often con- 
tinuous with the last-named sulcus, arches from before 
backwards through the centre of the surface, and sub- 
divides it into an upper division the SUPERIOR 
PARIETAL LOBULE, and a lower division the INFERIOR 
PARIETAL LOBULE (fig. 60, page 130). The inferior 
parietal lobule is again divisible into three parts an 
anterior part, arching round the posterior end of the 
fissure of Sylvus, and called the SUPRA-MARGINAL 
GYRUS ; a middle part, the ANGULAR GYRUS, behind 
the fissure of Sylvius, and continuous, round the hinder 
end of the parallel or superior temporal sulcus, with the 
middle temporal gyrus ; and a posterior, behind the 
angular gyrus, and called the POST-PARIETAL GYRUS 
(fig. 60, page 130). 

The angular gyrus probably contains the word-seeing 
centre the centre through which we remember what 
we see (figs. 39 and 42, page 64). The superior parietal 
lobule and the posterior part of the praecuneate lobe 
contain the centres called stereognostic centres, by 
means of which we recognise the form and solidity of 
objects. The central gyri the ascending frontal and 
parietal and the paracentral lobule contain the sen- 
sory-motor centres, the centres through which the mind 
differentiates and stores up its memories of muscular 
movements (figs. 39 and 42, page 64). The anterior 
central is, however, more directly motor, the posterior 
central more directly sensory. 



134 



THE CENTRAL NERVOUS SYSTEM 



TABLE OF GVRI OF PARIETAL LOBE. 





Posterior central 




- 


or ascending 




' Outer 
Surface 


s. parietal. 
Superior parietal 
lobule. 
Inferior parietal 


j Supra-marginal. 
-| Angular. 


Inner 


lobule. 
See mesial sur- 


Post-parietal. 


. Surface. 


face of hemi- 






spheres. 





Parietal lobe , 



(3) The Occipital Lobe. This lobe presents a 
greater number of individual variations in the arrange- 
ment of its gyri than any of the other lobes. Pyramidal 
in shape, with the apex or occipital pole backwards, 
it has three surfaces an external, in contact with the 
parietal and occipital bones ; an internal, forming part 
of the mesial surface of the hemisphere; and an in- 
ferior, continuous with the under surface of the 
temporal lobe, and resting on the upper surface of 
the tentcrium cerebelli. At present we shall notice 
the external surface only ; the others will be described 
with the corresponding surfaces of the hemispheres. 

The external surface is bounded in front by the 
EXTERNAL PARIETO-OCCIPITAL FISSURE, and by a line 
drawn downwards from this fissure across the surface 
to a notch caused by the temporal bone on the lower 
margin of the hemisphere (fig. 60, page 130). The 
other boundaries of the external surface are the margins 
of the hemisphere. Two transverse sulci divide the 
surface into three antero-posterior gyri a SUPERIOR, 
a MIDDLE, and an INFERIOR OCCIPITAL (fig. 60, page 
1 30) ; but these convolutions are by no means constant, 
and no two brains seem alike, with a corresponding 



BRAIN, CEREBRUM, CONVOLUTIONS 135 

difference in description in different books. In the ape 
the external surface of the occipital lobe is bounded in 
front by a distinct cleft, and this is sometimes repre- 
sented in man by a small sulcus the sulcus lunatus. 

The inner aspect and the posterior part of the 
outer aspect of the occipital lobes contain the centres 
connected with sight (fig. 42, page 64). 

TABLE OF GYRI OF OCCIPITAL LOBE. 

} Superior. 

Outer surface j- Middle. 

J Inferior. 
Occipital lobe 

Inner surface See inner surface. 

Under surface See next section. 

(4) The Temporal Lobe (fig. 60, page 130), occupy- 
ing the middle fossa at the base of the skull, is conical 
in shape, its anterior end being called the temporal pole. 
It has three surfaces an upper, a lower, and an external 
or lateral. 

The external surface is bounded above by the 
FISSURE OF SYLVIUS, which separates it from the 
parietal lobe ; below by the inferior temporal sulcus, 
which separates it from the under surface. Behind, 
there is no definite line of demarcation between it and 
the outer surface of the occipital lobe the line pro- 
longed downwards from the external parieto-occipital 
fissure serving as its limit. This surface has three 
antero-posterior fissures the superior, the middle, and 
the inferior temporal ; the upper two sulci separate, 
from each other, the SUPERIOR, the MIDDLE, and the 
INFERIOR TEMPORAL GYRI. The inferior fissure is, as 



136 



THE CENTRAL NERVOUS SYSTEM 



we have said, the boundary between the outer and the 
lower surfaces. 

The upper surface of this lobe is hidden within 
the fissure of Sylvius, and is marked out by some- 
what inconstant sulci into two or three indefinite 
transverse gyri. The superior temporal gyrus, along 
with the fore part of the upper surface of the temporal 
lobe, contains the centres associated with hearing (fig. 39, 
page 64). 

The inferior surface presents a transverse depres- 
sion caused by the upper margin of the petrous part 
of the temporal bone, and this may be taken as the 
limit between the temporal and the occipital lobes 
the part in front of the groove being convex, and 
belonging to the temporal lobe ; the part behind the 
groove being concave, and belonging to the occipital 
lobe. These two parts are taken together under the 
term occipito - temporal, and their gyri are two in 
number a SUPERIOR and an INFERIOR OCCIPITO-TEM- 
PORAL, separated from each other by the collateral 
fissure (see fig. 62, page 130). The fore part of this 
surface of the temporal lobe contains the cortical 
centres for taste (fig. 42, page 64). 



TABLE OF GYRI OF TEMPORAL LOBE. 
External surface 



Temporal lobe ' 



Lower surface 



Upper surface 



Superior temporal. 
Middle temporal. 
Inferior temporal. 

/ Superior and inferior 
t occipito-temporal. 



Two or three transverse 
gyri. 



BRAIN, CEREBRUM, CONVOLUTIONS 137 

The Central Lobe. Insula Isle of Reil (fig. 63, 
page 130), lies deeply placed within the fissure of 
Sylvius, and cannot be seen unless the sides of that 
fissure be drawn apart. Pyramidal in shape, with its 
apex directed downwards, forwards, and outwards, it 
consists of five or six convolutions called GYRI-OPERTI, 
which, in front and behind, are separated by well-marked 
sulci from the temporal and frontal lobes respectively. 
Externally, a deep cleft the sulcus centralis separates 
the insula from the overlapping gyri, collectively called 
the operculum, formed by the contiguous ends of the 
ascending frontal, ascending parietal, inferior frontal, 
superior temporal, and external orbital convolutions. 
The- surface of the insula is subdivided by the sulcus 
centralis, which runs from its apex to its base, into a 
frontal part, consisting of three or four short gyri 
gyri breves : and a temporal part, composed of two 
long gyri gyri longi. At. the apex of the insula is a 
small area, the limen insula, which connects the grey 
matter of the insula with the grey matter of the anterior 
perforated space (see fig. 63, page 130). 

II. Fissures, Lobes, and Gyri of the Mesial Surface. 
(fig. 62 page 130). Most of the convolutions of this 
surface are parts of lobes already described, but it will be 
well to group them together under the above heading. 
To examine them you will require a mesial vertical section 
of the brain, with the cerebellum removed. 

Arching through the middle of this aspect of the 
hemisphere is the cut surface of the corpus callosum, 
which divides the area into an upper division, plane 
and vertical, which faces inwards and consists of the 
mesial aspects of the frontal, parietal, and occipital 
lobes; and a lower division, already noticed on page 136, 



138 THE CENTRAL NERVOUS SYSTEM 

which is concave and convex from behind forwards, and 
looks downwards and inwards. It consists of the under 
aspects of the occipital and temporal lobes. These two 
divisions will be taken together, the corpus callosum 
being used as the guide to the study of the fissures 
and convolutions. 

The CALLOSAL SULCUS or sulcus corporis callosi 
commences in front below the anterior end of the 
corpus callosum. It runs along the upper margin of 
the corpus callosum, and then turns round its posterior 
extremity, and skirting the inner border of the temporal 
lobe, ends in the notch of the uncus. Between the 
callosal fissure and the upper margin of the hemispheres, 
lies the sulcus cinguli or calloso-marginal sulcus, which, 
commencing in front beneath the anterior end of the 
corpus callosum, extends backwards, parallel to the 
margin of the hemisphere, to the level of the hinder 
end of the corpus callosum, where it turns upwards 
to the mesial border of the hemisphere, a little behind 
the fissure of Rolando (fig. 62, page 130). It limits 
the extent of the frontal lobe on this surface of the 
hemisphere. The original direction of the sulcus 
cinguli is continued by a small fissure sulcus sub- 
parietalis which along with the sulcus cinguli, separates 
the gyrus cinguli or gyrus fornicatus below, from the 
marginal gyrus and the quadrate lobe above. 

The GYRUS CINGULI or gyrus fornicatus convolu- 
tion of the corpus callosum (fig. 62) commences in 
front below the anterior end of the corpus callosum, 
and, arching upwards and backwards over the body 
and round the posterior end of the corpus callosum, 
becomes slightly constricted the isthmus and then 
runs downwards and forwards, on the mesial edge of 



BRAIN, CEREBRUM, CONVOLUTIONS 139 

the temporal lobe, as the GYRUS HIPPOCAMPI. It is 
also called the UNCINATE GYRUS, from the hook-like 
process uncus gyri hippocampi in which it ends in 
front (fig. 62, page 130). The uncinate gyrus contains 
the cortical centre for smell. The gyrus cinguli, the 
gyrus hippocampi, and the uncus, together, form the 
limbic lobe. This lobe, along with the olfactory lobe, 
constitutes the rhinencephalon or olfactory brain. 

The MARGINAL CONVOLUTION (fig. 62, page 130), 
belonging, as we have seen, to the upper part of the 
mesial surface of the frontal lobe, begins at the 
base of the cerebrum, at a spot called the anterior 
perforated space, and, skirting the upper edge of the 
hemisphere above the sulcus cinguli, becomes continuous 
above with the superior frontal gyrus, and below with 
the gyrus rectus of the orbital surface. Behind, it is 
limited by the vertical part of the sulcus cinguli (fig. 62, 
page 130). The hindermost part of the marginal gyrus 
is called the paracentral lobule (fig. 62, page 1 30) : it is the 
mesial aspect of the ascending frontal convolution. 

The INTERNAL PARIETO-OCCIPITAL FISSURE (fig. 62, 
page 130) lies behind the vertical part of the sulcus 
cinguli, the two enclosing between them the mesial 
surface of the parietal lobe, called the QUADRATE LOBE 
or PRyECUNEUS (fig. 62, page 130). 

Below the internal parieto-occipital fissure is the 
calcarine fissure (fig. 62, page 130), which runs forwards 
from the posterior border of the hemisphere to join the 
internal parieto-occipital fissure. Together these two 
fissures enclose the wedge-shaped mesial aspect of the 
occipital lobe, called the CUNEATE LOBE or CUNEUS 
(fig. 62, page 130). Sometimes the calcarine fissure 
winds backwards round the occipital pole, and appears 



1 40 THE CENTRAL NERVOUS SYSTEM 

on the outer aspect of the occipital lobe behind the 
sulcus lunatus. 

The HIPPOCAMPAL SULCUS or sulcus dentatus (fig. 62, 
page 130), continuous behind with the callosal sulcus, 
ends in front, as we have already seen, in the notch 
of the uncus. It separates the hippocampal gyrus from 
the fimbria or tania hippocampi, which will be seen in 
the descending horn of the lateral ventricle. 

The COLLATERAL SULCUS, running below and 
parallel with the hippocampal sulcus, separates, as we 
saw on page 136, the superior and inferior occipito- 
temporal convolutions from each other. The fore part 
of the superior occipito-temporal convolution has been 
already noticed under the names hippocampal and 
uncinate gyri. The hinder portion of the convolution, 
that which lies beneath the calcarine sulcus, is called 
the LINGUAL LOBE. The inferior occipito-temporal 
convolution, lying beneath the collateral sulcus, and 
separated from the outer aspect of the temporal lobe 
by the inferior temporal sulcus, is usually called the 
FUSIFORM LOBE, though this name is often confined 
to the posterior part of this gyrus. 

The FASCIA DENTATA or dentate convolution is a 
notched gyrus, the free edge of the superficial grey 
matter of the hemisphere (fig. 62, page 130). It 
lies at the bottom of the dentate fissure, and is 
continuous, in front, with a small band band of 
Giacomini which crosses the uncus of the gyrus 
fornicatus, and, behind, with a thin, grey lamina, the 
fasciola cinerea, and, through it, with the mesial and 
lateral longitudinal stria; of the corpus callosum. It 
is part of an abortive convolution which can be seen 
on opening up the fissure of the corpus callosum, and 
its continuation, the dentate fissure. 



BRAIN, CEREBRUM, RHINENCEPHALON 141 



Gyri of Mesial 
Surface 



TABLE OF THE GYRI OF THE MESIAL SURFACE. 

Gyrus fornicatus or gyrus cinguli. 
Hippocampal and Uncinate gyri. 
Dentate gyrus. 
Marginal gyrus. 
Paracentral lobule. 
Praecuneus or Quadrate lobe. 
Cuneus or cuneate lobe. 
Lingual lobe. 
Fusiform lobe. 

The Rhineneephalon or olfactory brain, consists of 
an anterior part the olfactory lobe (see page 139): and 
a posterior part the limbic lobe (see page 139). 
Although of physiological interest these tracts are not 
of great clinical importance. Their constituents will 
therefore be given in the form of a table for reference 
only. 

TABLE OF OLFACTORY BRAIN--RHINENCEPHALON. 

1. Olfactory bulb. 

2. Olfactory peduncle. 

Olfactory LobeJ 3. Olfactory trigone and its tubercle. 

4. Olfactory area of Broca. 

5. Subcallosal gyrus. 

6. Anterior perforated spot. 

f Gyrus cinguli. 
Cingulum. 
Isthmus gyri 

fornicati. 

Hippocampal gyrus. 
Uncus, 

Fascia dentata. 
Fimbria. 



Limbic 
Lobe. 



1. Gyrus fornicatus. 

2. Mesial and lateral 

longitudinal striae. 

3. Fornix. 

4. Corpora mammillaria. 

5. Anterior commissure. 

6. Septum lucidum. 

7. Medullary striae. 

8. Nucleus habenula;. 



142 



THE CENTRAL NERVOUS SYSTEM 



The various methods for locating these fissures and 
convolutions in relation to the scalp and to the skull 
will be found in your surgical works. 



SUMMARY OF THE FUNCTIONS OF THE CORTICAL 
CENTRES OF THE CEREBRUM (see tig 39, page 64). 

I. The MOTOR AREAS occupy the ascending frontal 
convolutions, not only on their superficial aspects, but 
also on that aspect which forms the anterior wall of 
the fissure of Rolando, for both these areas have layers 
of giant cells, but no distinct granular layers (see 
page 147). 

The following is the position of the chief motor 
centres enumerated from below upwards: 



I. Head 


f i. Tongue. 

r() 


Lips. 


3. Trunk, f 9- Chest. 
I 10. Abdomen. 


and 


2. Face. < (b} 


Larynx. 




Neck. 


3. Neck. 


Eyes. 






14, Fingers. 




In. Hip. 




5. Hand. 
6. Wrist. 
7. Elbow. 




12. Knee. 
13. Ankle. 
14. Foot. 




8. Shoulder. 




15. Toes. 



II. The SENSORY AREAS for 

1. Common Sensibility sensory discrimination 
occupies the ascending parietal convolution, including 
the posterior wall of the fissure of Rolando, which has 
many granular cells but no giant cells. 

2. Special Senses 

i. Speech Broca's Convolution. 



BRAIN, CEREBRUM, CORTICAL CENTRES 143 

2. Smell uncinate gyrus and the limen of the 

isle of Reil. 

3. Taste tip of the temporal lobe. 

4. Hearing superior temporal convolution and 

the fore part of the upper surface of the 
temporal lobe. 

5. Sight cuneate gyrus, round the calcarine 

sulcus ; the occipital pole and the part of 
its outer surface behind the sulcus lunatus. 

6. Word-seeing centres through which we 

remember what we see angular gyrus or 
posterior part of the inferior parietal lobule. 

7. Stereognostic sense the centres through 

which we recognise the size, shape, and 
position of objects quadrate or praecuneate 
lobes. 

III. The PSYCHICAL AREAS, or areas of association, 
occupy the chief parts of the rest of the lobes and 
convolutions of the cerebrum. They cannot be 
stimulated from without, and are as yet but little 
understood. 

SUMMARY OF THE VASCULAR SUPPLY OF THE 
CORTICAL CENTRES. 

1. The cortical areas for touch, for speech, and for 
hearing, and part of the cortical centre for sight are 
supplied by the middle cerebral arteries. 

2. The cortical and the sub-cortical areas for motion, 
are also supplied by the middle cerebral artery ; but 
that part of the cortical motor centre for the lower 
limbs which is situated in the paracentral lobule and in 
the contiguous part of the anterior central gyrus, is 
supplied by the anterior cerebral arteries. 



144 THE CENTRAL NERVOUS SYSTEM 

3. The visual paths and the hemicentres for sight 
are supplied by the posterior cerebral arteries. 

STRUCTURE OF THE CORTEX OF THE CEREBRUM. 

(Fig. 64 and 65, Plate XIX., Page 144.) 

The Grey Matter of the cerebral cortex is arranged 
in several more or less distinct layers, composed of 
nerve-cells and nerve-fibres, of neuroglia, of blood- 
vessels, and oi lymphatic spaces. 

Seen with the naked eye a vertical transverse section 
of the cerebral cortex shows six strata, alternately white 
and grey three white and three grey. The white 
layers correspond to regions in which there are many 
nerve-fibres gathered into transverse bundles, the grey 
layers to parts in which there are few such nerve-fibres. 

Of these white layers, the most superficial one is 
called the line of Bechterein ; the two deeper ones are 
named the lines of Baillarger. In the occipital lobe 
a somewhat similar and very characteristic layer is 
called the line of Gennari. 

With the aid of the microscope four layers of the 
cortex are usually described according to the kinds of 
nerve-cells met with in the various layers. Enumerated 
from without inwards they are (i) the molecular or 
superficial layer or stratum zonale ; (2) the layer of 
small pyramidal cells; (3) the layer of large pyramidal 
cells ; and (4) the layer of polymorphous cells. 

i. The Molecular Layer. This layer contains 
many neuroglia-cells. Its. nerve-cells are of three 
kinds : 

(i) Polygonal Cells, which are scattered throughout 
the layer. They have several protoplasmic processes 
and an axis cylinder - process, which has either a 



Fu;. 64 Cerebrum Structure. 

Fusiform Triangtilar Polygonal 

cell.. 




PLATE XIX. 



FIG. 65. 



. l'ia mafer. 



V^- **V ^^ Molecular 
layer. 






\ 

luiyer of 




Polymorphous layer. 



' L|u> 



BRAIN, CEREBRUM, STRUCTURE 145 

horizontal or an ascending direction. They end free 
in this layer. 

(2) Fusiform Cells ovoid in shape, with their long 
axis horizontal, hence called horizontal cells (Cajal). 
They are bipolar, and have protoplasmic processes 
passing from each end of the cell. At some distance 
from the cell one of these processes gives rise to a 
long axis-cylinder process, which ends free within this 
layer. 

(3) Triangular Cells, which usually have three proto- 
plasmic processes and several axis-cylinder processes. 
The axis-cylinder processes ascend and end in the 
molecular layer. 

2. Layer of Small Pyramidal Cells. The cells of 
this layer are of small and medium size, and as indicated 
by their names, are mostly pyramidal in shape, with 
their apices towards the surface. The cells which are 
situated next to the molecular layer are, however, 
polyhedral or star-shaped. In structure the pyramidal 
cells resemble the similar cells in the next layer. 

3. Layer of Large Pyramidal Cells. Cells of 
Betz giant cells. The cells of this layer are much 
larger than those of the last layer. They are pyramidal 
or polyhedral in shape, with their apices towards the 
surface and their bases towards the white substance. 
Each cell has an axis-cylinder and protoplasmic processes. 

The axis-cylinder process descends from the centre 
of the base of the cell towards the subjacent white 
substance. In the upper part of its course this process 
gives off, at right angles to its direction, many side 
branches collaterals which run horizontally and 
branch dichotomously. The branches are granular, 
and end free in little knobs. In the lower part of its 

L 



146 THE CENTRAL NERVOUS SYSTEM 

course the axis-cylinder process becomes tortuous, and 
gives off no collaterals. It ultimately ends in little 
tufts of branches in the grey matter at lower levels of 
the cerebro-spinal axis. 

The protoplasmic processes arise from the apex and 
from the lateral angles of the cells. They are beset 
with short thick spines (fig. 64, page 144). The hori- 
zontal branches cross and recross each other, and form 
a dense network. All the branches end free in little 
knobs or thickenings. 

4. Layer of Polymorphous Cells. In this layer 
(fig. 64, page 144) the cells vary much in size and in 
shape, being fusiform, ovoid, triangular, and star-shaped. 
They have ascending and descending protoplasmic 
processes. The axis-cylinder process, sinuous in its 
course, gives off collaterals and ends in the white 
substance, either by bending at right angles to its 
original direction, or by T or Y shaped junctions with 
the fibres of the white matter. 

Besides the several kinds of nerve-cells just described, 
there are throughout the last three layers of the cortex 
two other kinds of cells : 

1. Cells with short axis-cylinder processes cells of Golgi (fig. 64, 
Nos. 4 and 5, page 144) star-shaped, with branching protoplasmic 
processes, and with an axis-cylinder process, which, after a short 
course, ends free in dense tree-like branches. 

2. Cells with ascending axis - cylinder processes Martinotti. 
These cells are fusiform or globular in shape, and are mostly met 
with in the polymorphous layer. Besides their protoplasmic pro- 
cesses, they have an axis-cylinder process, which ascends from the 
apex of the cell towards the cortex, giving off collaterals on its way. 
Ultimately this process ends in the molecular layer in tree-like 
branches beset with small spines, knobbed at their extremities. 



BRAIN, CEREBRUM, BASE 147 

Many authors divide the cerebral cortex into eight or more 
layers according to the shape and size of the cells, viz. 



1. Molecular layer. 

2. Small pyramidal layer. 

3. Median pyramidal, super- 

ficial layer. 

4. Large pyramidal, super- 

ficial layer. 



5. Stellate layer. 

6. Large pyramidal, deep 

layer. 

7. Median pyramidal, deep 

layer. 

8. Polymorphous layer. 



The white and grey nerve-fibres found in the grey 
cortex are the protoplasmic and axis-cylinder processes 
of the nerve-cells of the cortex, or of those at lower 
levels of the nerve-axis. In structure they are like 
the nerve-fibres of the spinal cord. 

Neuroglia pervades the entire cortex, especially 
along the line of its vessels. In structure it is similar 
to the neuroglia of the spinal cord described on page 34. 
It forms a special superficial stratum under the pia mater. 

The blood-vessels and lymphatic spaces of the 
cerebrum have already been described on page 61. 

The above may be regarded as the typical structure 
of the chief parts of the cerebral cortex ; but there are 
many differences in structure in different regions, these 
differences indicating, in all probability, differences in 
function ; thus in the motor cortex there are groups of 
very large pyramidal cells, the giant cells, or cells of 
Betz; in the sensory cortex, especially in the auditory 
and in the visual areas, there are no such cells, but 
numberless small granular cells. 

II. BASE OF THE CEREBRUM. 
(Fig. 66, plate XX., p. 148). 

Though the heading of this section is " Base of the 
Cerebrum," it will be as well to consider the base of the 



i 4 8 THE CENTRAL NERVOUS SYSTEM 

entire brain, and not confine ourselves merely to the 
under surface of the cerebrum. 

The Base or under aspect of the brain is, as we 
have already seen, very irregular in shape, for it is 
moulded on the inner aspect of the base of the cranium. 
In connection with it we recognise the following 
structures: (i) the cerebellum; (2) the medulla; (3) 
the pons Varolii ; (4) the cerebral peduncles or crura 
cerebri ; (5) the under aspect of the frontal, temporal, 
and occipital lobes ; (6) part of the great longitudinal 
fissure and of the fissure of Sylvius ; (7) the anastomos- 
ing circle of blood-vessels the circle of Willis ; (8) the 
interpeduncular space; (9) the lamina cinerea ; and (10) 
the superficial attachments of the cranial nerves. Most 
of these structures have already been described in the 
preceeding pages. At present we shall examine more 
particularly the interpeduncular space, the lamina 
cinerea, and the surface attachments of the cranial nerves, 
leaving their deep connections to be studied in the 
section on the "Origins of cranial nerves," page 197. 

The INTERPEDUNCULAR SPACE is the irregular, 
depressed area, at the centre of the base of the cerebrum, 
between the great longitudinal fissure in front, the 
under surface of the frontal and temporal lobes at the 
sides, and the pons and cerebral peduncles behind. 
Lozenge-shaped in outline, it is covered in by a 
delicate layer of grey and white matter, called the 
lamina cinerea, which stretches across the middle line, 
and unites the under aspects of the hemispheres. 

In front, the interpeduncular space is bounded by 
the sharp anterior border of the corpus callosum, called 
the rostntm, and by two narrow bands the peduncles of 
the corpus callosum, which, hidden within the anterior 



PLATE XX. 



Great longitudinal 
fisswe. 



FIG. 66. 



Lamina terminalis. 

Locus perforator 
anticus. 

Infundibulwm,. 

Tuber tinerewn. 

Corpora 
Afammiliaria. 




11 n. 



12 . 



Spinal root of 
spinal accessory. 



Medulla 
oblongata. 



Cerebellvm. 



Base of Brain. 



BRAIN, CEREBRUM, BASE 149 

mesial fissure, run backwards and outwards towards 
the fissure of Sylvius. Behind, the space is limited by 
the upper border of the/^wj, and by the diverging cerebral 
peduncles. At the sides, it is continuous with the 
under aspects of the frontal lobes. Its floor is formed 
by the thin layer of grey and white matter the 
lamina cinerea. 

The LAMINA CINEREA or interpeduncular lamina, 
lozenge-shaped like the space which it fills, is almost 
vertical in front, but slopes upwards and backwards 
behind. Unlike the rest of the cerebral cortex it is 
not convoluted, but retains the original non-convoluted 
character of the cerebral surface. At one time it 
formed the floor of the primitive fore-brain, it now 
forms the floor of the 3rd ventricle. It consists of two 
halves, right and left, which are united in the middle line. 
Its edges and its angles blend with the edges and 
angle of the space it covers, and its grey matter is continu- 
ous, at the back, with the grey matter of the aqueduct of 
Sylvius, at the sides, with the grey matter of the island 
of Reil. Though one continuous membrane, it has 
received different names in different parts of its extent, 
and, connected with it and with the interpeduncular 
space, are the following structures. 

In front, between the rostrum and peduncles of the 
corpus callosum, the two halves of the lamina cinerea 
are united across the middle line by a very slender, 
translucent portion, called the lamina terminalis, origin- 
ally the central part of the anterior, terminal wall of the 
neural tube, now the anterior wall of the 3rd ventricle. 
Passing across the middle line, behind the lamina 
terminalis and adherent to it, is a transverse white 
band of nerve- fibres, the OPTIC CHIASMA or COMMISSURE, 



1 50 THE CENTRAL NERVOUS SYSTEM 

which, at the sides, is prolonged forwards and outwards 
into two rounded bundles, the OPTIC NERVES, and 
backwards and inwards as two flattened white strands, 
the OPTIC TRACTS, which curve round the outer sides 
of the cerebral peduncles. 

External to the optic commissure, at the root of 
the fissure of Sylvius, and behind the olfactory 
peduncles, are two triangular, shallow depressions, one 
on each side the ANTERIOR PERFORATED SPACES 
(fig. 66, page 148), greyish laminae, perforated for the 
passage of the blood-vessels into the interior of the 
cerebrum. These perforated, grey laminae are con- 
tinuous internally with the lamina cinerea ; externally 
with the grey 'matter of the island of Reil. Across 
them run the peduncles of the corpus callosum, and 
the external roots of the olfactory peduncles. In the 
middle line, behind the optic commissure, is a small 
grey elevation, the TUBER CINEREUM, from which a 
funnel-shaped process, the INFUNDIBULUM. projects 
downwards, capped at its apex by the posterior lobe 
of the PITUITARY BODY (fig. 67 page 152). 

Behind the tuber cinereum, between it and the 
cerebral peduncles, we find two small rounded, pea-shaped 
nodules, the CORPORA MAMMILLARIA or ALBICANTIA 
which, we shall afterwards see, are closely connected 
with a band of association fibres called the fornix. 
Between the corpora mammillaria and the tuber 
cinereum is a small, vascular, trefoil- shaped eminence 
the EMINENTIA SACCULARIS homologous with the 
saccus vasculosus of lower vertebrata. Behind the 
corpora mammillaria, between the diverging cerebral 
peduncles, lies the POSTERIOR PERFORATED SPACE 
pons Tarini a grey lamina, similar to the anterior 



BRAIN, CRANIAL NERVES 151 

perforated space, and, like it, perforated for the passage 
of blood-vessels into the interior of the cerebrum 
(fig. 66, page 148). 

Thus we see that the optic commissure with its 
prolongation backwards and forwards, forms a St 
Andrew's Cross, dividing the interpeduncular space 
into four areas ; one in front of the cross, filled in by 
the lamina terminalis ; one behind the cross, containing 
the tuber cinereum, the infundibulum, the pituitary body, 
the corpora mammillaria, the eminentia saccularis and 
the posterior perforated spot ; and one on each side of 
the cross, the anterior perforated spots, crossed by the 
peduncles of the corpus callosum and by the outer limbs 
of the olfactory peduncles. Some authorities confine the 
term interpeduncular space to the interval between the 
cerebral peduncles and the optic commissure, naming 
this area the opto-peduncular space. 

CRANIAL NERVES. Their superficial origins or 
terminations (fig. 66, page 148). 

1. In the olfactory groove, on the under aspect of 
the frontal lobe, lies the olfactory bulb, often called 
the ist nerve. To it are attached the olfactory 
nerves from the olfactory mucous membrane of the 
nose. 

2. Springing from the fore and outer part of the 
optic commissure, on each side, are the optic nerves 
the 2nd nerves. 

3. At the upper or anterior border of the pons, 
internal to the crura cerebri, are the 3rd nerves, or 
motores oculi. 

4. At this same border, but external to the cerebral 
peduncles, are the 4th nerves pathetici. 

5. At the side of the pons, where it becomes the 



THE CENTRAL NERVOUS SYSTEM 



middle peduncle of the cerebellum, are the 5th nerves 
the trifacial, or trigeminal. 

6. At the lower border of the pons, near the middle 
line, are the 6th nerves abducentes. 

7. At a little distance from the middle line are the 
7th or facial and 8th or auditory nerves. 

8. On the side of the medulla, behind and external to 
the olivary body, are the 9th nerves glosso-pharyngeal, 
loth nerves vagus, and iith nerves spinal accessory, 
in this order from above downwards. 

9. In front of and internal to the olivary body arise 
the 1 2th or hypoglossal nerves. 



TABLE OF CRANIAL NERVES. 



ist nerve. 

2nd 

3 r d 

4th 

5th 

6th 

7th 



8th 



9th 
loth 
nth 
1 2th 



Olfactory . 

Optic 

Oculo-motor 

Patheticus or Trochlearis 

Trigeminus or Trifacial 

Abducens . 

Facial 

Pars intermedia 

Auditory . 



Glosso-pharyngeal 

Vagus 

Spinal Accessory 

Hypoglossal. 



sense of smell. 

sense of sight. 

motor. 

motor. 

mixed i.e., motor and 

sensory, 
motor, 
motor, 
sensory. 
Cochlear division 

hearing. 
Vestibular division 

equilibrium, 
mixed, 
mixed, 
motor, 
motor. 






BRAIN, CEREBRUM, INTERIOR 153 

TABLE OF OBJECTS SEEN ON THE BASE OF THE BRAIN. 
(Fig. 66, Plate XX., Page 148.) 

' (a) Posterior perforated spot. 

(b) Corpora mammillaria or 
albicantia. 

(c] Eminentia saccularis. 

(</) Hypophysis cerebri or 
pituitary body. 

(e) Infundibulum. 

(/) Tuber cinereum. 

(g) Optic commissure optic 
nerves optic tracts. 



1. The Cerebellum. 

2. The Medulla. 

3. The Pons. 

4. The Crura Cerebri. 

5. Interpeduncular space. 

6. Anterior perforated spots. 

7. Corpus Callosum rostrum 

peduncles. 

8. The Cranial Nerves. 



(h) The lamina cinerea. 
9. Under aspects of frontal, temporal, and occipital lobes. 

10. Fissura cerebri lateralis or fissure of Sylvius, and part of 

great longitudinal fissure. 

1 1 . Blood-vessels Circle of Willis. 

III. INTERIOR OF THE CEREBRUM. 

Dissection page 48. 
(Fig 68, Page 158; Fig. 72, Page 166.) 

GENERAL OUTLINE. Above the level of the corpus 
callosum, the cerebral hemispheres consist of a solid, 
white, central core centrum ovale minus, composed of 
strands of nerve-fibres, surrounded externally by a 
wavy layer of grey matter the cerebral cortex. 

Ventricles. Below the level of the corpus callosum, 
however, the interior of the cerebrum is occupied by a 
large, irregular cavity, the remains of the neural canal 
from the walls of which the brain and spinal cord were 
developed. Somewhat T-shaped in coronal section, 
this cavity is subdivided by partitions into smaller 
spaces called VENTRICLES. Thus we have (i) the 3RD 
VENTRICLE, a vertical, mesial, longitudinal, cleft-like 



154 THE CENTRAL NERVOUS SYSTEM 

space represented by the upright stroke of the T 
lying beneath the corpus callosum, and extending 
below to the base of the cerebrum ; and (2) two lateral 
diverticula, the LATERAL VENTRICLES, the cross stroke 
of the T hollowed out in the substance of each hemis- 
phere. Uniting these various ventricles with each other 
are narrow passages or channels, constricted portions of 
the original neural tube. Thus, in front, we find the 
INTERVENTRICULAR FORAMINA, or the foramina of 
Monro, which connect the lateral ventricles with the 
3rd ventricle, and, through that ventricle, with each other : 
behind, on the other hand, is the passage called the 
AQU^EDUCTUS CEREBRI aqueduct of Sylvius or iter 
a tertio ad .quartum ventriculum (fig. 67, page 152). 

Basal Ganglia. Besides the white nerve-matter and 
the central cavity, the interior of the cerebrum is also 
occupied by large collections of grey matter ganglionic 
masses, the sub-cortical or basal ganglia the chief of 
which are the CORPORA STRIATA, which belong to the 
telencephalon ; the OPTIC THALAMI and the CORPORA 
GENICULATA, which belong to the diencephalon ; and 
the CORPORA QUADRIGEMINA, which belong to the 
mesencephalon. Each hemisphere, therefore, forms a 
kind of shell enclosing and overlapping the basal 
ganglia. 

Nerve-strands. Finally, uniting together the cerebral 
hemispheres and their ganglia are various strands of 
nerve-fibres the FORNIX, the CORPUS CALLOSUM, and 
the ANTERIOR, MIDDLE, and POSTERIOR COMMISSURES. 

We shall describe (i) the VENTRICLES, with their 
communications and septa ; (2) the BASAL GANGLIA ; 
(3) the COMMISSURES and other STRANDS of NERVE- 
FIBRES. 



BRAIN, CEREBRUM, VENTRICLES 155 

I. VENTRICLES OF THE BRAIN. 

(Dissection Page 48). 
(Figs. 68, etc., Plates XXII., etc., Pages 158 to 166). 

The Ventricles of the brain are usually described 
as five in number, but, in reality, there are only four 
viz. the TWO LATERAL 1st and 2nd ; the THIRD and 
the FOURTH. These four ventricles are the remnants 
of the neural canal, and are continuous with each other 
and with the ventricle or central canal of the spinal 
cord. The 5th ventricle, on the other hand, belongs to 
a different category, and the term ventricle as applied 
to it is somewhat misleading, for it has none of the 
characters of the other ventricles, being neither a part 
of the original neural tube, nor lined by the same 
epithelium as the rest, nor in any way connected with 
them in the adult. It will be noticed along with the 
septum lucidum. The 4th ventricle has already been 
described at page 119. 

THE LATERAL VENTRICLES. 

(1st and 2nd.) 
(Fig. 68, Page 158; Fig. 70 Page 160). 

The LATERAL VENTRICLES, or ventricles of the hemi- 
spheres, are two irregular crescent-shaped cavities, 
right and left, hollowed out in the substance of the 
cerebral hemispheres. Placed back to back, but 
separated, in the middle line by a thin, vertical partition, 
each ventricle consists of a central part or BODY, and 
of three prolongations or recesses called the ANTERIOR, 
the POSTERIOR and the LATERAL HORNS. 

The Body of the Ventricle is the highest and 
largest portion of the cavity, and, whether looked at 



156 THE CENTRAL NERVOUS SYSTEM 

from above or in coronal section, is triangular in form, 
for it is wider behind than it is in front, and wider 
above than it is below. Moreover it is deeper in front 
than behind, and deeper near the middle line than at 
the sides, where the roof and the sloping floor meet 
and blend with the substance of the hemispheres. 

The roof of the lateral ventricles is formed by the 
CORPUS CALLOSUM. 

The floor presents from before backwards (a) a 
small part of the CORPUS CALLOSUM where it turns 
downwards and backwards in the longitudinal fissure ; 
(b} next a club-shaped eminence the NUCLEUS 
CAUDATUS of the corpus striatum ; (c) behind this an 
oval grey mass the upper surface of the OPTIC 
THALAMUS, which is separated from the nucleus 
caudatus by a shallow groove in which lies (d) the 
STRIA TERMINALIS or tcsnia semicitcularis. Resting on 
the optic thalamus is (e) a fringe of blood-vessels the 
CHOROID PLEXUS of the lateral ventricles ; and, finally, 
close to this fringe, but nearer the middle line, is (/) 
the sharp, sickle-shaped, free edge of the BODY of 
the FORNix. 

The inner wall of the ventricle is formed by a 
thin, double, vertical, triangular, mesial, longitudinal 
partition the SEPTUM LUCIDUM which extends 
between the corpus callosum and the fornix. Behind, 
however, the septum lucidum tapers to a point and 
the floor, formed by the fornix, and the, roof formed by the 
corpus callosum, come in contact and blend together in the 
middle line, therefore we no longer have an inner wall. 

Externally also, the floor, which slopes upwards and 
outwards, meets the roof in the mass of the hemi- 
spheres, thus leaving no outer wall. 



BRAIN, CEREBRUM, VENTRICLES 157 

The Cornua of the Ventricles are six in number 
three on each side anterior, posterior, and lateral or 
descending (figs. 70, etc., page 160). 

1. The Anterior Cornu is a short conical, curved, 
horn-shaped recess, which turns forwards and outwards 
from the forepart of the body of the ventricle, round 
the anterior end of the nucleus caudatus into the 
substance of the frontal lobe. 

Its roof, its anterior wall, and its floor are formed 
by the CORPUS CALLOSUM ; its inner wall by the 
SEPTUM LUCIDUM ; while behind it is limited by the 
NUCLEUS CAUDATUS of the corpus striatum. 

2. The Posterior Cornu is a similar recess, passing, 
at first, outwards then backwards and inwards into 
the substance of the occipital lobe. 

Its roof is formed by some of the fibres of the 
CORPUS CALLOSUM, which as they spread out over the 
horn like a carpet, are called the tapetum ; its floor is 
formed by the substance of the occipital lobe. In the 
floor is an oval prominence the HIPPOCAMPUS MINOR, 
caused by the calcarine sulcus seen on the mesial surface 
of the hemisphere. Above and internal to the hippo- 
campus (fig. 75, p. 170) is a slight ridge the BULB of the 
POSTERIOR HORN due to a special bundle of radiating 
fibres of the corpus callosum, called the forceps major. 

3. The Lateral Cornu descending or inferior 
horn curves round the posterior end of the optic 
thalamus as a bent finger-like passage with its con- 
vexity outwards. At first it runs backwards and out- 
wards, then downwards, forwards, and finally inwards 
(B.O.D.F.I.) in the substance of the temporal lobe (fig. 
70, page 1 60). 

In its roof arc the tapetum of the CORPUS CALLOSUM ; 



158 THE CENTRAL NERVOUS SYSTEM 

the posterior extremity of the OPTIC THALAMUS; the 
taenia semicircularis or STRIA TERMINALIS; and, finally, 
the tapering end of the NUCLEUS CAUDATUS, which, 
at the anterior end of the horn, swells out and unites 
with the nucleus amygdalae. 

In the floor of the passage lies a curved, elongated 
projection, following the bend of the horn, and called 
the HIPPOCAMPUS MAJOR or CORNU AMMONIS. Below, 
at the apex of the horn, the HIPPOCAMPUS ends in an 
enlarged, grooved, pawn -like extremity the PES HIPPO- 
CAMPI ; while along its inner concave margin runs a 
thin, white, tapering band of nerve-fibres the T/ENIA 
HIPPOCAMPI or FIMBRIA, the prolongation of the 
posterior pillars of the fornix. Above and internal 
to the fimbria is the CHOROID PLEXUS of the lateral 
ventricles, which, at this point, indents the epithelial 
wall of the ventricular cavities along the lateral part of 
what is known as the great transverse fissure of the 
cerebrum (see page 165). Below and internal to 
the fimbria is the free edge of the grey matter of 
the cortex, which, owing to the notched appearance 
caused by the passage over its free edge of the branches 
of the choroidal artery, receives the name FASCIA 
DEN TATA. 

At the point where the lateral and posterior horns 
diverge from each other, you will find a triangular 
area the trigonum ventriculi marked by a slight 
eminence the EMINENTIA COLLATERALS varying in 
size in different subjects. It is caused by the collateral 
fissure on the surface of the cerebrum (fig. 75, page 
170). 

Ependyma Ventriculorum. The lateral ventricles 
are lined by a layer of neuroglia, covered on the surface 



PLATE XXII. 



Lateral Ventricles. 
FIG. 68. 



N.C. 



S.T. 




C.C. Corpus ccMosum. 

N.C. Nucleus caudahu of corpus striatum. 

S.T. Stria, terminalis 

O.T. Optic thalamus. 

C.P. Char end plexus. 

F. Fomix posterior pillar. M c L4 9 n i Cu 



BRAIN, CEREBRUM, VENTRICLES 159 

by a layer of columnar ciliated epithelium, continuous 
with the epithelium of the other ventricles. 

Communications. Between the fornix in front and 
the optic thalami behind are two slit-like openings, one 
on each side the foramina of Monro (fig 67, page 152). 
By means of these openings the two lateral ventricles 
communicate directly with the 3rd ventricle, and in- 
directly, i.e. through the 3rd ventricle, with each other. 
Through these same foramina, the choroid plexuses 
of the lateral ventricles are continuous with those of 
the 3rd ventricle. 

THE 3RD VENTRICLE. 

Dissection, Page 49. 
(Fig. 72, Page 166; Fig. 77, Page 178.) 

The 3RD VENTRICLE is the deep, narrow, vertical, 
cleft- like space which is situated in the middle line 
of the cerebrum, between the two optic thalami. It lies 
beneath the velum interpositum and the body of the 
fornix, and extends down to the base of the brain, 
being deeper in front than behind. 

Boundaries. The roof is formed by a layer of 
flattened epithelial cells, which covers the under surface 
of the VELUM INTERPOSITUM. 

Its floor, which, at first, slopes from behind down- 
wards and forwards, then upwards and forwards, is formed 
by the dorsal part of the cerebral peduncles, by the 
lamina cinerea, and by the other structures contained 
within the interpeduncular space at the base of the 
cerebrum, viz., the LOCUS PERFORATUS POSTICUS, the 
CORPORA MAMMILLARIA, the EMINENTIA SACCULARIS, 
the TUBER CINERUM.the INFUNDIBULUM, the PITUITARY 
BODY, and the OPTIC CHIASMA. 



160 THE CENTRAL NERVOUS SYSTEM 

In front, the ventricle is limited by the COLUMNS 
FORNICIS or Anterior Pillars of the Fornix, by the 
ANTERIOR COMMISSURE,and by theLAMINATERMINALIS; 
behind, by the AQU^.DUCTUS CEREBRI or acqueduct of 
Sylvius, by the POSTERIOR COMMISSURE, and above this 
by the base of the PINEAL GLAND. At the sides the 
walls of the cavity are formed by the inner or vertical 
faces of the OPTIC THALAMI, along each of which runs 
a bundle of white fibres the PEDUNCLES of the PINEAL 
GLAND. Crossing the centre of the space, between the 
optic thalami, is a delicate, broad, grey band the 
MASSA INTERMEDIA the middle, soft or grey com- 
missure. In the floor, between the lamina terrninalis 
and the optic chiasma, is a slight recess, the optic 
recess. 

The 3rd ventricle is lined by columnar epithelium 
similar to, and continuous with, that of the other 
ventricles. On the roof, however, the epithelium is 
flattened, and follows all the folds of the vascular fringes 
the choroid plexuses which hang down along the 
middle line from the under surface of the velum 
interpositum. The lateral walls of the ventricle are 
covered by a layer of ependyma, and the floor consists 
of grey matter continuous with the grey matter of the 
aquaeductus cerebri. This grey matter comes to the 
surface of the brain at the lamina cinerea. 

Communication. The 3rd ventricle communicates 
in front, through the INTERVENTRICULAR foramina 
(Monro) with the lateral ventricles ; behind, through 
a narrow passage the AQU^DUCTUS CEREBRI (Sylvius) 
with the 4th ventricle ; and below, at the fore part 
of the floor, by a conical-shaped passage with the 
infundibulum ITER AD INFUNDIBULUM. 



PLATE XXII 



Cerebrum Lateral Ventricle. 



F.Afi. 



G.C.C. 



M.L.S. 




A.C. Anterior comu. 

N.C. Nucleus caudatut. 

8.T. Stria terminaUs. 

O.T. Optic thalumus. 

C.P. Choroid plexus. 

H.Mi. Hippocampus minor 

l\C Posterior comu. 



F.Mi. Forceps minor. 
G.C.C. Genu corpvris cattosi. 
M.L.S. Median longitudinal stria. 
B.C.C. Body wrporis caUosi 
S.C.C. Splenium corporis callosi. 
F.Ma. Forceps major. 
T. Tapetum M' i.< * cui '" 



PLATE XXIV. 



Cerebrum Lateral Ventricles. 
FIG. 70. 



C.C. 



H.Ma. 




5th V. 5th Ventricle. 

N.C. Nucleus caudatus. 

(J. P. Choroid plexus. 

O. T. Optic thalamus. 

F. Fornix. 

C.C. Corpus callosum. 

I'.C. Posterior cornu. 



A Alveus 

C. C. Corpus callosum. 
S.L. Septum lucidum. 
S. T. Stria terminalis. 
P.H. Pes hippocampi. 
H.Ma. Hippocampus major. 
T.H. Ttenia hippocampi. 

C.F. ' Orwrafftmicis. 
K C. Eminentia collateral!*. 
H.Afi. Hippocampus minor. 

M<Lfu team- 



BRAIN, PINEAL GLAND, PITUITARY BODY 161 

The 4th ventricle was described on page 119; but 
it would be well to re-read the section at this stage, so 
as to bring it in line with the other ventricles. 

The two following structures are associated with 
the 3rd ventricle : 

The Corpus Pineale or PINEAL GLAND (fig. 72, page 
166), is a reddish, vascular, oval, fir-cone shaped body, 
with its base directed upwards and forwards. It 
is situated in the middle line above the orifice of the 
aquaeductus cerebri, lying in the fore part of the 
longitudinal groove between the corpora quadrigemina. 
Firmly attached to the velum interpositum, which 
gives it a special covering, it is a backward prolongation 
of the cavity of the 3rd ventricle. To its base is 
attached a hlolow stalk, the lower segment of which 
unites the gland to the posterior commissure, whereas 
the upper segment divides into two white strands 
the peduncles of the pineal gland which run along 
the inner aspects of the optic thalami, ending in 
front by joining the medullary striae and the anterior 
pillars of the fornix. 

STRUCTURE The pineal body is composed of 
tubular follicles, separated by connective tissue. It is 
filled with epithelial cells, with corpora amylacea, and 
with calcareous particles, called brain sand. It contains 
a small cavity which communicates with the cavity 
of the 3rd ventricle. 

Pituitary Body or HYPOPHYSIS CEREBRI is 
usually left in the sella turcica when removing the 
brain. Oval in shape with its long axis transverse, 
it has a reddish colour, and consists of two lobes an 
anterior and a posterior, separated from each other by 
the pars intermedia. The anterior lobe, glandular in 

M 



i6a THE CENTRAL NERVOUS SYSTEM 

structure, consists of a network of connective tissue and 
of epithelial cells. It is originally a hollow prolongation 
from the pharynx, but subsequently becomes solid. 
The posterior lobe is a downward tubular prolongation 
of the floor of the diencephalon the cavity from which 
the 3rd ventricle is formed. It consists of a reticulum 
of fine nerve-fibres embedded in a network of connective 
tissue and neuroglia. The pars intermedia consists of 
epithelial cells like the anterior lobe. 

FUNCTIONS. The pineal gland, which was formerly 
regarded as a rudimentary third eye, is now known to 
be an important organ of internal secretion, its secretion, 
before the age of puberty, powerfully influencing the 
growth and nutrition of the organs of generation. The 
anterior lobe of \)s\, pituitary body also produces an internal 
secretion, which, in some way, modifies the general 
growth and nutrition of the body. The secretion of 
the posterior lobe, and of the pars intermedia, is 
colloid in character. 

The Septum Lucidum and the 5th Ventricle (Dis- 
section, page 48). The Septum Lucidum is the thin, 
double, vertical, mesial, longitudinal partition, composed 
of two layers, which separates the lateral Ventricles 
from each other (fig. 67, page 152; fig. 72, page 166; 
fig- 77- P a ge 178). Triangular in shape, it fills up the 
interval between the concavity of the knee-shaped bend 
of the corpus callosum, and the convexity of knee- 
shaped bend of the anterior pillars of the fornix. It is 
broader in front than behind, and gradually tapers to a 
point where the corpus callosum and fornix come in 
contact with each other. Between the two layers of 
which it is composed, it encloses a narrow slit-like 
cavity, the 5th VENTRICLE, or cavity of the septum, 



BRAIN, VELUM INTERPOSITUM 163 

which lies in front of, and at a higher level than the 
3rd ventricle. Internally, next the cavity of the 5th 
ventricle, each lamina of the septum is composed of a 
thin layer of grey matter, derived originally from the 
grey matter of the cortex. Externally, next the cavity 
of the lateral ventricles, each lamina of the septum 
consists of white matter, representing the medullary 
or white matter of the hemispheres, and, like the rest 
of the lateral ventricles, is covered by a layer of 
ependyma and epithelium. Thus we see that the 
cavity of the 5th ventricle is not a true ventricle, and 
is not lined by epithelium like the other ventricles, nor 
does it in any way communicate with them. 

As we shall see in the section on " Development," 
the septum lucidum was originally part of the wall 
of the hemispherical vesicle which became cut off 
from the general surface by the development of the 
corpus callosum and fornix (page 244). 

The Velum Interpositum. (Dissection, page 49) 
is a thin horizontal partition, which you have already 
seen in the roof of the 3rd ventricle, and in the floor 
of the lateral ventricles (fig. 73, page 168). It is a 
fold of pia mater, which enters the brain through what 
is known as the great transverse fissure of the cerebrum, 
thus appearing in the 3rd and lateral ventricles, though 
separated from their cavities by the epithelium of the 
ependyma. Triangular in shape, with its apex forwards 
and its base backwards, the velum interpositum has the 
same extent as the body of the fornix, so that it reaches 
from the foramen of Monro in front, to the back part 
of splenium of the corpus callosum behind, beneath 
which, after investing the pineal gland, it becomes 
continuous with the rest of the pia mater covering 



164 THE CENTRAL NERVOUS SYSTEM 

the cerebrum and cerebellum, (fig. 29, page 50). At 
the sides, the free edges of the velum interpositum, 
covered with epithelium, project into the floor of the 
lateral ventricles, and rest on the upper surfaces of the 
optic thalami. Round the hinder ends of the optic 
thalami the velum passes into the descending horns of 
the lateral ventricles, being still continuous with the pia 
mater of the rest of the brain. 

Choroid Plexus. (fig. 71, page 164; fig. 73, page 
168). The choroid plexus consists of tortuous ramifica- 
tions of small blood-vessels, branches of the choroidal 
artery, which are carried inwards with the velum inter- 
positum, and form a plexus of blood-vessels, covered 
with vascular papillae, and clothed with a layer of 
epithelium. Projecting downwards along the middle line 
of the under aspect of the velum interpositum are two 
of these vascular fringes the choroid plexuses of the 
3rd ventricle covered everywhere, however, by the 
epithelium which forms the roof of that cavity. In 
each lateral margin of the velum interpositum are 
similar vascular fringes the choroid plexuses of the 
lateral ventricles. They extend from the interventricular 
foramina or foramina of Monro, through which they 
are continuous with the plexuses of the 3rd ventricle, 
to the apex of the descending cornu of the lateral 
ventricles, where the velum interpositum becomes 
continuous with the rest of the pia mater through the 
great transverse fissure. As the vascular fringes pass 
down the lateral horns, they send a prolongation into 
the posterior horn. 

The Venae Cerebri Internse (fig. 73, page 168) are 
two veins which gather up the blood from the corpora 
striata and from the choroid plexuses. They run back- 



PLATE XXV. 



N.C. 



C.C. 



S.T. 



O.T. 




P.M. 



H.Ma. 



V.I. 



H.Mi: 



N.C. 

5.V. 

S.T. 

O.T. 

P.H. 

H.Ma. 

T.V. 

E. C. 

H.Mi. 

F.p.p. 

P.B. 



V.C.I. 



F.p.p. 



C. 



P.B. 



Nucleus caudatus. C. C. 

5M ventricle. S. L. 

Stria terminalis. F.a.p, 

Optic thalamus. P.H. 

Pes hippocampi. H. M. 

Hippocampus major. T.H. 

Trigonum ventriculi. F.D. 

Eminentia collateralis. C.P. 

Hippocampus minor. V.I. 

Fornix (posterior piUats) cut. I'. C. I. 

Pineal body. C. 



Corpus callosum. 

Septum lucidum. 

Fornix (anterior pilla,s)cut. 

Pes hippocampi. 

Hippocampus major. 

Tcenia hippocampi. 

Fascia dentata. 

Choroid plexus. 

Velum interpoaitum. 

Vena cerebri internet. 

Cerebellum. 



BRAIN, GREAT TRANSVERSE TISSUE 165 

wards, side by side, between the layers of the velum 
interpositum. Ultimately, uniting to form a single 
vessel, called the vena magnet, cerebri or vena Galeni, they 
discharge their blood into the straight sinus. 

The Great Transverse Fissure of the cerebrum 
(fig. 71, page 164) is the large artificial cleft which is 
made into the lateral ventricles when the pia mater 
and choroid plexuses, with the epithelium covering 
them, are torn away from the posterior part of the 
brain beneath the fornix, and from the descending 
cornua of the lateral ventricles. The fissure thus 
formed is horseshoe-shaped ; its central part corre- 
sponds to the base of the fornix, its lateral parts 
to the descending horns of the lateral ventricles. 
Through this fissure, (originally formed by the indenting 
and infolding of the mesial wall of the primitive 
cerebral vesicle, which along this line consists of a 
single layer of epithelium), the pia mater and choroid 
plexuses project into the ventricles, though, as we have 
before noted, everywhere separated from their cavity ;/ 
by the epithelium which covers them. The convex or 
posterior lip of the fissure is bounded near the middle 
line by the posterior part of the corpus callosum and 
fornix ; on each side by the free margins of the hemi- 
sphere viz. the fimbria and the fascia dentata. The 
concave or anterior lip of the fissure is bounded, near 
the middle line, by the corpora quadrigemina and cerebral 
peduncles ; on each side, by the posterior part of the optic 
thalami. 



166 THE CENTRAL NERVOUS SYSTEM 

II. BASAL GANGLIA. 

CEREBRAL SUB-CORTICAL GANGLIA. 

(Fig. 68, Plate XXII. Page 158; Fig. 75, Plate XXVIII. Page 170). 

Under this heading it is usual to describe the four 
large grey masses at the base of the brain, known as 
the corpora striata and the optic thalami. They are, 
however, quite distinct in their origin. The term, 
moreover, is often made to include the amygdaloid 
nuclei, the corpora quadrigemina, the corpora geniculata, 
and the locus niger. 

The amygdaloid nuclei are described with the 
corpora striata, on page 167 ; the corpora geniculata 
with the optic thalami, on page 170; the corpora 
quadrigemina and the substantia nigra with the 
pedunculi cerebri, on page 190. 

i. The Corpora Striata are two in number, one 
in each cerebral hemisphere. They are each subdivided 
into two parts, an intra-ventricular portion the nucleus 
caudatus which appears in the floor of the lateral 
ventricles ; and two extra-ventricular portions the 
nucleus lenticularis and the claustrum which are 
hidden in the white substance of the hemispheres 
(fig. 75, page 170, and fig. 77, page 178). 

The Nucleus Caudatus the intra-ventricular 
portion of the corpus striatum so called from its 
form (fig. 78, page 178), is the pear-shaped, kite- 
shaped, or pyriform eminence which appears in the 
fore part of the floor of the lateral ventricles. It has 
a pinkish colour though it is covered on the surface 
by a layer of white matter. Within, it consists of a 
grey core streaked with white fibres, hence the name 
corpus striatum (fig. 75, page 170). Its larger end or 



PLATE XXVI. 



V.C.I. 



Or.F. 



C.C. 



S.L. 



Cerebrum 3rd Ventricle. 




P.O. 



P. Cor. 



A . Cor. A nterior cornu. 

5th V. 5th Ventricle. 

N. C. Nucleus iMudatus. 

8. T. Stria terminalis. 

3rd V. 3rd Ventricle. 

O. T. Optic thalamns, 

P.B. Pineal body. 

C.Q. Corpora quadrigemina. 

V.C.I. Verne cerebri internal. 

Or.F. (Trura fornif-is. 



C.C. 

S.L. 

Col.F. 

A.C. 

M.I. 

P.C. 

P. 

V.I. 

C.P. 

P. Cor. 



Corpus callosum. 
Septum lucidum. 
Columnte fomicis. 
Anterior commissure. 
Afassa intermedia. 
Posterior commissure. 
Pulvinar. 

Velum interpositiim. 
Choroid plexus. 
Posterior cornu. 



BRAIN, CEREBRUM, BASAL GANGLIA 167 

head is directed forwards, and its posterior, tapering 
end or tail, passes backwards and downwards round 
the outer side of the optic thalamus, into the roof of 
the descending horn of the lateral ventricle. Ultimately 
the tail reaches the tip of the temporal lobe, where it ends 
by blending with the amygdaloid nucleus, an outgrowth 
of the cerebral cortex in this region. The nucleus 
caudatus may therefore be described as horse-shoe 
shaped, the horse-shoe being set edgeways, with its 
heels to the front, and the whole so tilted that the 
upper half of the shoe lies nearer the middle line than 
the lower half. Thus it forms an arch with its concavity 
forwards, one end of the arch being made by the head, 
the other end by the tail (fig. 78, page 178). 

The Nucleus Lentieularis the extra-ventricular 
part of the corpus striatum is placed external to both 
the nucleus caudatus and to the optic thalamus, being 
separated from them by a strand of white nerve-fibres, 
called the internal capsule (fig. 75, page 170; fig. 77, 
page 178). As it is hidden within the substance of 
the cerebral hemisphere, it cannot be seen unless we 
make a series of sections of the hemispheres (fig. 75 ( 
page 170; fig. 77, page 178). In horizontal sections 
it appears as a longitudinal grey mass, shaped like a 
double convex lens, hence the name lenticularis. In 
coronal section it is triangular in shape, with its base 
outwards. Intersected by two white lamina;, it is 
divided into three parallel strands internal, middle, 
and external of a somewhat different colour. The 
internal and middle portions have a paler hue, hence 
the name globus pallidus applied to them ; the external 
segment is darker in colour, and is called the putamen 
a pod, a peel, a shell (fig. 77, page 178). In front 



168 THE CENTRAL NERVOUS SYSTEM 

and below, at the base of the cerebrum, the nucleus 
caudatus and the nucleus lenticularis are continuous 
with each other, and with the grey matter at the 
anterior perforated space. 

Claustrum. External to the nucleus lenticularis 
is a narrow, longitudinal, vertical plate, sheet or band 
of grey matter the claustrum the bar or barrier. 
In sections it appears as a delicate, denticulated streak 
of grey matter, which is separated from the nucleus 
lenticularis by a strand of white nerve-fibres, the 
external capsule, and from the contiguous grey matter 
of the isle of Reil by a second white strand, the white 
matter of the isle of Reil (fig. 75, page 170, and fig. 77, 
page 178). Thus, enumerated from within outwards, we 
have 

(i) The nucleus caudatus. 

(2) The internal capsule. 
(3) The nucleus lenticularis. 

(4) The external capsule. 
(5) The claustrum. 

(6) The white matter of the isle of Reil. 
(7) The grey matter of the isle of Reil. 
The nucleus lenticularis, the claustrum, and the tail 
of the caudate nucleus are continuous below and in front 
with the amygdaloid nucleus, which, we have seen, is 
the thickened part of the cortex of the temporal lobe 
at the anterior end of the descending horn of the lateral 
ventricles. 

By some authors the claustrum is regarded as part 
of the lenticular nucleus, by others as a well-developed 
fifth layer of the cerebral cortex. 

2. The Optic Thalami bed-roomsare two large, 
oval, convex prominences, right and left, placed above 



Nucleus 

<:audatus. 



Choroid plexus: 



Velum 
interpositum. 



Velum Interpositum. 
FIG. 73. 



PLATE XXVII. 



h Ventricle. 




Venae cerebri 
internee. 



Vena Galeni. 



FIG. 74. 



Limbif. Lobe - /- 



Median 
Inn/fit A 'trine 



Band of Giacomini 



Fornix. 




Fascia dentata 



BRAIN, CEREBRUM, BASAL GANGLIA 169 

the cerebral peduncles, but behind and internal to the 
corpora striata, from which they are separated by the 
strtte terminates or taeniae semicirculares. Forming part 
of the floor of the lateral ventricle and the walls of the 
3rd ventricle, each optic thalamus consists of a central 
grey core, covered on the surface by a stratum of white 
matter, and, where they enter into the formation of the 
ventricular cavities, are clothed by ependyma and 
epithelium. They have four surfaces and two ends. 
Their anterior end expands into a rounded tubercle the 
anterior tubercle ; and their posterior end swells out into 
a much larger prominence the posterior tubercle or 
pulvinar (fig. 72, page 166) which forms part of the 
roof of the descending horn of the lateral ventricle, and 
overhangs the brachia of the corpora quadrigemina, 
and the two oval nodules called the corpora geniculata 
interna and externa (fig. 59, page 114). 

The upper or horizontal surface of the thalami optici 
is divisible into an outer part, which appears in the 
floor of the lateral ventricles, and a mesial part, on 
which rests the velum interpositum, with the choroid 
plexus in its outer free edge. The under surface, in its 
hinder part, is placed above the pedunculi cerebri, while, 
more in front, it lies over the corpus albicans and the 
tuber cinereum (fig. 67, page 152). 

The inner or mesial surfaces of the optic thalami are 
vertical, face towards each other, and form the lateral 
walls of the 3rd ventricle. Along them run the 
peduncles of the pineal gland, and below these 
peduncles, passing transversely between the optic 
thalami, is the massa intermedia, the middle or grey 
commissure. 

Externally the optic thalami are each limited by the 



170 THE CENTRAL NERVOUS SYSTEM 

nucleus caudatus and by the posterior part of the 
internal capsule. From this same aspect many nerve- 
fibres, which constitute the thalamic radiation, diverge 
in different directions to reach the cerebral cortex. 

In front of the optic thalami are the nucleus cajudatus 
of the corpus striatum, and the anterior pillars of the 
fornix, which ultimately pass to the base of the brain 
through the substance of tfie optic thalamus (fig. 67 } 
page 152). Finally, between the optic thalami and the 
anterior pillars are the slit-like clefts the inter- 
ventricular foramina or foramina of Monro, by means 
of which the lateral ventricles communicate with the 
3rd ventricle. 

Behind the optic thalami are the crura fornicis or 
posterior pillars of the fornix, which wind down the 
descending horn of the lateral ventricle (fig. 70, 
page 1 60). 

STRUCTURE. The optic thalami are chiefly com- 
posed of grey matter arranged as three nuclei anterior, 
outer, and inner. The course and relations of their white 
tracts are exceedingly complicated and are not yet fully 
understood. 

FUNCTIONS. The corpora striata are probably 
secondary centres connected with motion, for they can 
initiate automatic acts apart from the cerebral cortex. 
The optic thalami are secondary terminal stations of 
sensory fibres, apprising us of sensations but not dis- 
criminating them. 

Corpora Geniculata. Below and external to the 
pulvinar are, as we have said, two oval eminences 
the corpora geniculata interna and externa, so called 
from their resembling little knots on the optic tracts. 
The internal pair are smaller and mesial to the external, 



FIG. 75. 



PLATE XXVIII. 




P.C. 



A.C. 

N.C. 

S.T. 

C.C. 

O.T. 

C.P. 

H.Ma. 

T.H. 

E.G. 

P.C. 



Anterior cornu. 
Nucleus caudatus. 
Stria terminalis. 
Corpus caUosum. 
Optic thalamus. 
Char oid plexus. 
Hippocampus Major. 
Teenia hippocampi. 
Eminentia coUateralis 
Posterior cornu. 



N.L. Nucleus lentieularis. 
Ex. C. External capsule. 

Claustrum. 

White matter of I ale of Reil. 

Grey matter of Isle of Reil. 

Putamen. 

Optic thalamus. 

Trigonum ventriculi. 



'. C. Nucleus candatus. 
I. C. Internal capsule. 

a. Anterior limb. 

f. Genu. 

p. Posterior limb 



C. 

W.I. 

G.I. 

Pt. 

O.T. 

T.V. 



ff.P.C. Bulb 

of posterior 

cornu. 



H. Mi. Hippocampus minor. 



BRAIN, CEREBRUM, WHITE STRANDS 171 

and are separated from them by a band of white fibres, 
one of the roots of the optic tract (fig. 59, page 1 14). 

These geniculate bodies consist of a grey core and 
of a white cortex. To each proceeds a white band 
from the optic tracts. The band to the internal pair 
has, however, nothing to do with sight. Similar strands 
connect the external geniculate bodies to the anterior, 
and the internal geniculate bodies to the posterior pair 
of corpora quadrigemina. 

The Arterial Supply of the Basal Ganglia is derived 
from the anterior, middle, and posterior cerebral arteries. 
It will be more fully considered with the arteries to 
the Capsules, page 182. 

III. WHITE STRANDS. 

White Matter. The white nerve-substance of the 
cerebrum lies beneath the surface grey matter, and, like 
that of the spinal cord, is composed both of medullated 
and non-medullated nerve-fibres. The medullated fibres 
are transverse, longitudinal, and vertical in direction. 
They are the axis-cylinder processes of the nerve-cells 
of the various layers of the cortex, or of cells at lower 
levels of the cerebro-spinal system ; they are divisible 
into three groups, viz., (i) Commissural fibres ; (2) 
Association fibres ; and (3) Projection fibres. 

1. COMMISSURAL FIBRES are these which, passing 
across the middle line, unite the two halves of the same 
segment oT the brain or spinal cord. 

2. The chief COMMISSURES of the cerebrum are the 
corpus callosum, the anterior, middle, and posterior 
commissures. 



1 72 THE CENTRAL NERVOUS SYSTEM 

CORPUS CALLOSUM. 

Dissection, page 47. 
(Fig. 69, Plate XXIII, Page 160; Fig. 67 Page 152). 

The Corpus Callosum is, as you already know, the 
longitudinal white band of transverse nerve-fibres which 
arches from before backwards, in the middle line, 
between the two cerebral hemispheres, and connects 
them together. About four inches long, it forms the 
floor of the great longitudinal fissure, the roof and 
part of the floor of the lateral ventricles. It reaches 
further forwards than backwards, and is thicker at the 
ends than in the middle of its extent, being thickest 
and widest behind. 

Anteriorly, it turns downwards and backwards upon 
itself in the great longitudinal fissure, making a knee- 
shaped bend the GENU (fig. 67, page 152). Gradually 
becoming smaller it then forms a narrow, transverse, 
median band the ROSTRUM (fig. 67, page 152) which 
ends below at the base of the brain by bifurcating into 
two tapering processes the PEDUNCLES which can 
be traced to the anterior perforated spots at the root 
of the fissure of Sylvius, and to the uncinate gyri. 
Between these two peduncles lies the lamina terminalis. 

Posteriorly, on the other hand, the corpus callosum 
ends in a thickened, free, rounded border or base the 
SPLENIUM or pad (fig. 67, page 152). From each side 
of the outer ends of this pad, a horn-shaped bundle 
of fibres, the forceps major, turn backwards into the 
occipital lobe ; and a similar band, the forceps minor, 
can be traced, from each side of the genu, into the frontal 
lobes (fig. 69, page 160). 

The upper surface of the corpus callosum, covered 



BRAIN, CEREBRUM, CORPUS CALLOSUM 173 

by a thin layer of grey matter, is marked, along 
the middle line, by a longitudinal groove the raphe 
parallel to which, on each side, you will see two or more 
faint lines the median longitudinal stria or nerves of 
Lancisi (fig. 69, page 160, and fig. 74, page 168). Ex- 
ternally, under cover of the overhanging edge of the 
gyrus fornicatus or gyrus cinguli, are similar longitudinal 
striae lateral longitudinal strice the taeniae tectae or 
covered bands. The median striae, when traced 
forwards, are joined in front by a prolongation of the 
lateral striae, and descend with them round the anterior 
end of the corpus callosum to the peduncles of the 
corpus callosum ; behind, on the other hand, the striae 
can be traced into a fine grey lamina the fasciola 
cinerea and thence into the fascia dentata (fig. 74, 
page 1 68). The striae longitudinales, the fasciola cinerea, 
and the fascia dentata form an abortive convolution 
connected with the sense of smell. They are referred 
to on page 141. 

In the middle line, the under surface of the corpus 
callosum rests, in the posterior half of its extent, upon 
the upper surface of the body of the fornix, to which 
it is closely adherent, especially near the splenium. 
In its anterior half, its under surface is connected, in 
the middle line, with the vertical mesial partition the 
septum lucidum which fills up, as we have seen, the 
space left between the fornix behind and concavity of 
the knee-shaped bend of the corpus callosum in front 
(fig. 67, page 152, and fig. 72, page 166). 

Laterally, the transverse fibres of the corpus 
callosum, at first, form a compact strand which roofs over 
the lateral ventricles, but afterwards they spread out 
into the white substance of the hemispheres, threading 



i 7 4 THE CENTRAL NERVOUS SYSTEM 

their way between the fibres of the corona radiata, to 
reach the cerebral cortex. 

STRUCTURE The corpus callosum consists of white 
nerve- fibres which are, in the main, transverse,' a few 
only being longitudinal. The transverse fibres, as they 
pass into the hemispheres, diverge in all directions, and 
go, along with the fibres of the corona radiata, to the 
grey matter of the cortex. They start from the 
pyramidal cells of the one or the other side of the 
cerebral cortex, and end in ramifications in the 
pyramidal and molecular cell-layers of the opposite 
side. Many of them are derived from the optic thalamus, 
others are collaterals from the projection system of 
fibres. 

It is worthy of note that the corpus callosum may 
be absent without any ill effect. 

The anterior, middle, and posterior commissures are 
connected with the 3rd ventricle (fig. 67, page 152; 

fig- 7 2 , P a g e l66 )- 

The Anterior Commissure is a round white cord 
which passes transversely across the middle line in 
front of the anterior pillars of the fornix, between them 
and the lamina terminalis. It connects together the 
two olfactory lobes, and the two temporal lobes. 

The Massa Intermedia the middle or grey 
commissure crosses the 3rd ventricle between the 
optic thalami. It is a delicate band of grey matter 
connected with the grey matter of the thalami optici. 

The Posterior Commissure, situated in front of 
and below the pineal gland, but above the com- 
mencement of the passage into the 4th ventricle, is 
a rounded band which stretches between the back portion 
of the optic thalami. Its connections are very uncertain. 



BRAIN, CEREBRUM, FORNIX 175 

II. The ASSOCIATION FIBRES are, as you know, those 
which unite together different parts of the same 
hemisphere. Of these the fornix and the cingulum are 
the chief bundles ; the minor strands are given in the 
table, page 178. 

THE FORNIX. 

(Fig. 70, Plate XXIV. Page 160). 

Beneath the back part of the corpus callosum, and 
more or less adherent to it, especially behind, are two 
lateral longitudinal strands of association fibres, which 
blend together in the central part of their course, but 
remain separate in front and behind, where they bend 
down towards the base of the brain and form an arch or 
fornix with four pillars, two in front and two behind. 
This arched white band with its four pillars, is one of 
the chief pathways of the sense of smell, for its fibres 
can be traced from each hippocampus major to the 
corresponding corpora mammillaria. The fibres of 
which it is composed spring as two riband-like bands 
the FIMBRI^; one on each side, from the uncinate 
gyrus of the temporal lobe. Ascending along the 
concave edge of the hippocampus major, and being 
augmented by a fan-shaped set of fibres, called thealveus, 
from free surface of the hippocampus, the two bands or 
pillars CRURA FORNICIS wind round the posterior 
ends of the optic thalami, and converging towards 
each other, meet in the middle line to form a wide, 
flattened, triangular-shaped plate of white matter the 
BODY of the fornix which has its apex directed 
forwards towards the septum lucidum, and its base 
backwards towards the splenium of the corpus callosum. 

Above, the body of the fornix is in contact 



1 76 THE CENTRAL NERVOUS SYSTEM 

with the under surface of the corpus callosum ; 
below, it lies on the delicate lamina the velum 
interpositum which separates it from the optic thalami 
and from the 3rd ventricle. Behind, by its base, it 
blends, in the middle line, with the splenium of the corpus 
callosum, and, by its lateral angles, it is continuous 
with the crura fornicis. In front, its fibres diverge and 
go downwards and forwards from the apex of the body, 
as two cylindrical, finger-like processes lying side by 
side the anterior pillars or COLUMNyE FORNICIS which 
can be traced to the base of the brain, to the corpora 
mammillaria. In this course they lie first in front of, 
then in the substance of the optic thalami, but behind 
the anterior commissure, which separates them from 
the lamina terminalis. At the base of the brain, the 
pillars make an 8-shaped twist on themselves, form 
the cortex of the corpora mammillaria, and end in the 
grey core of these white bodies. From this core new 
fibres take their origin and either ascend, as the bundle 
of Vicq d'Azyr, to the optic thalami, or descend to the 
cells of the tegmentum of the crura cerebri (fig. 81, 
page 1 88). In front other fibres are given by the 
fornix to the septum lucidum, to the olfactory peduncle, 
and to the anterior perforated space. Between the 
optic thalami and the anterior pillars of the fornix 
there is, on each side, as already explained, a small 
circular foramen the interventricular foramen or the 
foramen of Monro. 

At the sides the body of the fornix has sharp, 
free, sickle-shaped edges. These rest upon the velum 
interpositum, in contact with, and overlapped by its 
fringed borders, and entering like them into the 
formation of the floor of the lateral ventricles, 



BRAIN, CEREBRUM, FORNIX 177 

Where the crura or posterior pillars of the fornix 
diverge from each other, there will be found a triangular 
space filled up by transverse fibres of white matter. 
It is called the lyra or psalterium, and the transverse 
fibres are commissural between the two hippocampi. 
Sometimes the fornix is entirely blended with the 
posterior part of the under surface of the corpus callosum ; 
at other times a small interval, called the ventricle of 
Verga, is left between them. 

Thus we see that originally the fornix consisted of 
two separate divisions, right and left, but that these 
ultimately fuse in the middle line to form the body 
of the fornix, their ends remaining free as the anterior 
pillars or columnae fornicis, and as the posterior pillars 
or crura fornicis. From its connections with the 
olfactory bulb in the one case, and with the uncinate 
and hippocampal gyri in the other, it is evident that 
the fornix is one of the chief pathways of the sense 
of smell. 

The Stria Terminalis Tcenza Semicircularis is 
the narrow white band which lies in the groove 
between the nucleus caudatus and the optic thalamus. 
In front, it joins the corresponding pillar of the fornix ; 
behind, it passes into the substance of the roof of the 
descending horn of the lateral ventricle and ends in 
the nucleus amydalae. 

The CINGULUM is the band of association fibres 
which lies beneath the mesial edge of the gyrus cinguli, 
and arches from before backwards, parallel with the 
convex surface of the corpus callosum. It extends 
from the anterior perforated space to the hook of the 
uncinate gyrus. 






178 THE CENTRAL NERVOUS SYSTEM 

The other groups of association fibres are given in 
the following table : 

TABLE OF ASSOCIATION FIBRES. 

1. Fibres which unite adjacent convolutions. 

2. Fibres which unite more distant convolutions, viz.: 

(a) Superior longitudinal fasciculus, which connects the 

convolutions of the frontal, temporal, and occipital lobes. 

(b) Inferior longitudinal fasciculus runs through the entire 

length of the temporal and occipital lobes and unites 
their convolutions. 

(c) Uncinate fasiculus connects the frontal pole and the 

orbital convolutions with the temporal.pole. 

(d) The perpendicular fasciculus has a vertical course in 

front of the occipital lobe. It connects the inferior 
parietal lobule with the fusiform lobe. 

III. PROJECTION FIBRES are those which pass from 
one segment of the cerebro-spinal system to another 
segment of the same system. They may be crossed or 
uncrossed. The chief groups of the projection systems 
of fibres, are contained in the internal and external 
capsules. 

INTERNAL AND EXTERNAL CAPSULES. 

Dissection page 49. 
(Fig. 75, Plate XXVIII, page 170). 

In treating of the Basal Ganglia, you will remember, 
we referred to two strands of white fibres, the INTERNAL 
and EXTERNAL CAPSULES, the former lying internal 
to, the latter external to the nucleus lenticularis. 
These so-called capsules are of the greatest clinical 
importance, for through them travel the chief motor 
and sensory tracts on their way to or from the cerebral 
cortex. 

The Internal Capsules (fig. 75, page 170), one in 
each hemisphere, when seen in horizontal sections, 



KIG. 76. 
Wall of Lateral Ventricle. 



PLATE XXIX. 




\--Optic thatamtis. 



Anterior cerebral a^ 
Middle 

Later, ventricle. 

CoLwn nafornicis. 

Rnndle of 
Vicq d"Azyr 

White matter \ 
ofinsuid. 

Internal 
capsule. 

External. 

Sni Ventricle. 
Anterior i^mmitutnr> 



r'fAr, 



FIG. 77. 



cerebral a. 
Pout, emnmnnicati'ng a. 



Corpus cnUosu.ni. 
Commissurcti fibres. 
Nucleus caudatus. 



Septum luciduvi. 

Optic, thalliums. 
Projection 

fibres. 
I Innvla. 



C'lanstrum. 

Association 

fibres. 




Head. Body. Tail, 
of Caudate nucleus. 



U- L(u * Cumming I 



BRAIN, CEREBRUM, CAPSULES 179 

appear as longitudinal, semi-lunar or crescent-shaped 
bands of white matter, with the convexities of the 
crescents directed towards the middle line. They 
can each be divided into three portions an anterior, 
a middle, and a posterior. The anterior division or 
ANTERIOR LIMB lies between the nucleus caudatus 
and the nucleus lenticularis ; the posterior division or 
POSTERIOR LIMB lies between the optic thalamus and 
the nucleus lenticularis, and forms, where the two 
divisions meet, a blunt angle or knee-shaped bend, the 
middle division or GENU. Each internal capsule, there- 
fore, has three parts: (i) a knee-shaped bend or the 
genu ; (2) a part in front of the knee, the pars frontalis ; 
and (3) a part behind the knee, the pars occipitalis. 
These capsules contain all the fibres of the fore part 
of the crura cerebri of the same side, except those 
that end in the basal ganglia. In the capsules the fibres 
from the crura are compressed sideways, forming two 
longitudinal white strands, with grey matter on each 
side. On emerging from these capsules, the fibres of 
the crura cerebri, reinforced by the fibres from the optic 
thalamus and the region below it, diverge in all 
directions, and radiate fanwise, towards the cerebral 
cortex, around the central hollow or ventricle, thus 
forming an inverted, hollow cone or crown of radiating 
fibres the CORONA RADIATA which spread out in all 
directions like lines of light from an exploded rocket. 

CONSTITUTION OF THE CAPSULES. The internal 
capsules contain the following sets of fibres : 

(a) The tracts forming the knee, and the anterior 
two-thirds of the posterior limb of the inner capsule 
are motor in function, and are in relation, from before 



i8o 

backwards, with the centres for the muscles of the eyes, 
mouth, tongue, face, upper limbs, trunk, and lower 
limbs respectively. Injury to this portion .of the 
internal capsule results in loss of motion on the 
opposite side of the body. 

(b) Mingled with the motor fibres are others which 
connect the central convolutions with the nucleus pontis, 
and, through this nucleus, with the cerebellum of the 
opposite side. This tract is a secondary motor tract. 
It is ultimately connected with the anterior spinal 
nerve-roots of the opposite side to that at which it 
left the brain. 

(c) The posterior third or more of the hinder division 
of the internal capsule contains sensory strands; for, 
when injured or diseased, there ensues loss of sensation, 
general and special, on the opposite side of the body, 
the motor powers not being affected, unless the lesion 
implicates the motor tracts also. These sensory strands, 
however, unlike the motor, do not form compact 
bundles, but are mingled with the motor fibres to the 
lower limbs. 

(d) Behind the above-named sensory strands are (i) 
the fibres of the optic radiation, connected with the 
centres for sight (fig. 80, pa^e 188) ; (2) the fibres of 
the auditory radiation, connected with the centres for 
hearing; and (3) the temporo - occipito -pontine fibres, 
from the temporal and occipital lobes to the nucleus 
pontis. 

Thus we see that the posterior limbs of the internal 
capsules and the regions immediately behind them carry 

(1) Sensations of touch, of temperature, and of pain ; 

(2) Sensations from muscles and from joints ; 

(3) Sensations of sight and of hearing. 



BRAIN, CEREBRUM, CAPSULES 181 

In connection with the positions of the motor fibres 
for the upper limb, it may be well to note that the 
arrangement is different in the internal capsule from 
what it is in the cerebral cortex (see page 142); for 
whereas in the cerebral cortex, from below upwards we 
have the centres for the 

Fingers, wrist, elbow, shoulder ; 

in the capsule, from before backwards, we have the 
fibres for the 

Shoulder, elbow, wrist, fingers. 

Note, therefore, that they are in the same order from 
above downwards in the cortex, as they are from 
before backwards in the capsules : moreover, in the 
cortex, the centres for the fingers are next the head, 
whereas, in the capsule, the centres for the shoulders 
are next the head. 

The Anterior Limb of the internal capsule, that 
part in front of the knee-shaped bend, carries (i) fibres 
between the basal ganglia ; (2) fibres from the cortex 
of the frontal lobe to the basal ganglia cortico-striate 
tracts and vice versa; (3) the thalamic radiations; 
(4) fibres from the fore part to the cerebral cortex to 
the pons fronto-pontine tracts ; and, finally, (5) through 
the red nucleus, fibres from the superior peduncles of 
the cerebellum. 

The External Capsule is the thin longitudinal 
strand of white matter which lies between the nucleus 
lenticularis and the claustrum. It mostly consists of 
association fibres, though the tracts which compose it, 
and their functions are undecided. 



1 82 THE CENTRAL NERVOUS SYSTEM 

ARTERIAL SUPPLY OF THE CAPSULES AND THE 
BASAL GANGLIA. 

When describing the middle cerebral artery, 
page 62, we saw that it gave off a ganglionic system 
of branches the lenticular, lenticulo-striate, and the 
lenticulo-optic. The lenticular artery supplies the 
inner and middle portions of the lenticular nucleus, 
and the internal capsule : the lenticulo-striate artery is 
distributed to the outer part of the lenticular nucleus ; 
to the external capsule, and to the caudate nucleus, 
though the fore part of the caudate nucleus is also 
supplied by the anterior cerebral arteries. The lenticulo- 
optic artery goes to the outer and posterior part of the 
nucleus lenticularis, and to the outer part of the optic 
thalamus. The optic thalamus is also supplied, in part, 
by the posterior cerebral and posterior communicating 
arteries. The lenticulo-striate artery is the one most 
commonly associated with cerebral haemorrhage. 

Fig. 76, plate XXIX. page 178, will give you an 
idea of the arterial supply to the capsules and to the 
basal ganglia. 

IV. CRURA CEREBRI. 

Dissection, page 49. 
(Fig. 54, Plate XIV. Page 96). 

The crura or pedunculi cerebri belong to that 
subdivision of the brain called the mesencephalon, 
or mid-brain. This subdivision also comprises the 
corpora quadrigemina, the lamina quadrigemina, and 
the aqueduct of Sylvius. 

The Cerebral Peduncles (fig. 43, page 72) are 
the two short cylindrical masses which you see spring- 



BRAIN, CRURA CEREBRI 183 

ing, in front, from the upper surface of the pons. They 
occupy the tentorial notch of the cranial dura mater, 
and are often called the isthmus cerebri for they connect 
the medulla and pons below with the cerebrum above. 
Diverging from each other, and enlarging as they 
ascend, they soon enter the base of the cerebral hemi- 
spheres and bury themselves beneath the optic thalami. 
On their ventral aspect the crura are convex trans- 
versely and striated vertically. Though, in front, they 
are separated from each other by a shallow, vertical, 
mesial groove or fossa, they are, in the greater 
part of their extent, blended together into one mass, 
the only line of division between them being a mesial 
raphe. 

Between the peduncles, in the shallow fossa where 
they diverge from each other, will be found the posterior 
perforated space and the two little white bodies, the 
corpora mammillaria (fig. 59, page 114). On their inner 
side is a longitudinal groove, the oculomotor groove, 
from which the 3rd nerve takes its superficial origin. 
On their outer side, marking off the crura from the 
region of the corpora quadrigemina, is a vertical sulcus 
the sulcus lateralis continuous below, but at an 
obtuse angle, with the groove which separates the 
superior from the middle peduncles of the cerebellum. 
Issuing from this sulcus and ascending obliquely across 
the superior peduncles to the posterior pair of corpora 
quadrigemina, is a faint strand of nerve-fibres the 
lateral fillet part of the central auditory tract. Above, 
winding round the outer side of the crura, near where 
they enter the cerebrum, are the optic tracts; and 
round them, below, where they emerge from the pons, 
are the slender 4th nerves. 



184 THE CENTRAL NERVOUS SYSTEM 

On their dorsal aspect the crura cerebri are sur- 
mounted by four rounded tubercles the corpora quad- 
rigemina which rest on the lamina quadrigemina, 
beneath which runs the aquaeductus cerebri (Sylvius). 

CONSTITUTION OF THE PEDUNCULI CEREBRI. A 
transverse section at right angles to the cerebral ped- 
uncles, will show you that they each consist of two 
portions, a posterior or dorsal the TEGMENTUM, and 
an anterior or ventral the CRUSTA, PES or BASIS. 
These two parts of the crura are separated from each 
other by a narrow stratum of grey matter, called, from 
its dark colour, the SUBSTANTIA NIGRA, or LOCUS 
NIGER, the position of which is indicated on the surface 
by the oculomotor groove internally, and by the lateral 
sulcus, externally (fig. 54, page 96). 

The constitution of the cerebral peduncles is given 
in the subjacent table : 

TABLE OF THE CONSTITUTION OF THE PEDUNCULI CEREBRI. 

The Cerebral Peduncles consist of two parts, a dorsal part, 
the tegmentum, and a ventral part, the crusta. 
1. Tegmentum. 

A. Its grey matter consists of 

(a) Scattered nerve-cells in the formatio recticularis. 

(b) Two specific groups of nerve-cells. 

(1) the red nucleus. 

(2) the stratum griseum, (.., , , , 

' I Nucleus of 3rd nerve, 
stratum centrale, or I XT . , , 

, < Nucleus of 4th nerve, 
grey matter of the| TT , , . 

, . I Upper nucleus of 5th nerve, 
aquaeductus cerebri. \ 

B. Its white matter consists of 
i. Longitudinal fibres. 

(i) Brachia conjunctiva or Superior peduncles of the 
cerebellum. 

((i) Main fillet or lemniscus, giving 
off upper fillet. 
(2) Lateral fillet. 



BRAIN, CRURA CEREBRI 185 

(3) Anterior longitudinal bundle tecto-spinal tract. 

(4) Posterior longitudinal bundle. 

(5) Spino-thalamic and spino-tectal tracts. 

(6) Rubro-spinal tract, prepyramidal, Wonakow's bundle. 

(7) Descending root of the 5th cranial nerve. 

(8) Olivary bundle. 

2. Transverse fibres, viz. those of the 3rd and 4th cranial 
nerves. 

I 1 . Crusta or Basis. 

(1) Pyramidal tracts. 

((<i) Fronto-pontine. 

(2) Cortico-pontine tracts. \ (b') Temporo-pontine. 

\.(c} Occipito-pontine. 

(3) Caudate cerebellar tracts. 

III. Substantial nigra or locus niger, separating the crusta from 

the tegmentum. 

I. The Tegrnentum (fig. 54, page 96) is the larger 
division of the crus, and, like the formatio reticularis 
of the medulla and pons, is composed of a reticulum 
of longitudinal and transverse fibres interspersed with 
grey matter. We shall study, first, the grey, then the 
white matter of the tegmentum. 

A. The GREY MATTER of the tegmentum consists 
of the formatio recticularis, continuous with that of the 
pons and medulla. In this reticulum we find both 
(a) scattered nerve-cells ; and (b} two definite collections, 
one being the STRATUM GRISEUM or the grey matter 
of the aqueduct of Sylvius ; the other the RED NUCLEUS 
or nucleus tegmenti (fig. 54, page 96). 

(1) The Red Nucleus lies beneath the anterior pair 
of corpora quadrigemina. It consists of multipolar 
nerve-cells, and is the primary termination of the 
superior cerebellar peduncles. 

(2) The Stratum Griseum, or grey matter of the 
aquaeductus cerebri, extends through the entire length 
of the Sylvian aqueduct. Its gives origin to the 3rd and 



i86 THE CENTRAL NERVOUS SYSTEM 

4th cranial nerves. Lying a little more external is 
the upper nucleus of origin of the 5th cranial nerve. 

B. The WHITE MATTER consists of longitudinal 
and of transverse nerve-fibres. 

i. Of the Longitudinal Fibres the chief strands 
are as follows: 

(i) The Brachia Conjunctiva, or superior peduncles 
of the cerebellum are the two semi-lunar shaped 
strands of nerve-fibres, which, at first, lie lateral, then 
ventral to the grey matter of the aqueduct of 
Sylvius. Traced from the sides and roof of the 4th 
ventricle, they ascend to the level of the corpora quad- 
rigemina, where most of the fibres decussate with 
these of the opposite side, a few only remaining 
on their own side. After crossing, the fibres ascend to 
end in the red nuclei, their primary terminations. From 
the cells of these nuclei three new strands take their 
origins, one set ascends and courses along the anterior 
limb of the internal capsule to the optic thalamus, and, 
through it, to the cerebral cortex. Another set, by way 
of the rubro-spinal tract, reaches the cells of the 
anterior horn of the spinal cord of the opposite side. 
A third group go to the nuclei of the motor cranial 
nerves, especially to the nuclei of the 3rd cranial nerve. 
Thus we see that the brachia conjunctiva form 
crossed tracts between the cerebellum of the one side, 
and the red nucleus, the optic thalamus, and cerebral 
cortex of the opposite side. Moreover, as we shall see 
in the next section, the brachia conjunctiva, through 
the rubro-spinal tracts, which are also crossed tracts, 
unite the cerebellum of the one side with the cells of 
the anterior horn of the spinal cord of the same side. 
(2) The Tract of tke Fillet, which in the upper part 



BRAIN, CRURA CEREBRI 187 

of the pons was a flattened strand of longitudinal fibres 
occupying the ventral part of the formatio-reticularis, 
in the crura forms a bundle of oblique fibres on the 
outer side of the red nucleus (fig, 54, page 96). When 
traced upwards from the pons it divides into two 
strands the Main Fillet and the Lateral Fillet. 

The Main Fillet or Lemniscus is as you know, the 
chief sensory strand from the medulla to the optic 
thalamus and thence to the cerebral cortex. 

The Lateral Fillet is the upward continuation of 
central auditory path from the opposite cochlear nucleus. 
On reaching the crura cerebri it diverges sideways to 
the sulcus lateralis, from which it emerges, as a series 
of fine fibres, which cross the superior cerebellar 
peduncles, and end in the nuclei of the posterior 
corpora quadrigemina. 

(3) The Anterior or Ventral Longitudinal Bundle 
tecto-spinal tract lies close to, but in front of the 
posterior longitudinal bundle. Its fibres start in the 
nuclei of the anterior pair of corpora quadrigemina, and, 
after decussating with their fellows of the opposite 
side in the mesial raphe, descend through the red 
nucleus, through the pons and medulla. Giving col- 
lateral to motor nuclei on their way, they reach the 
lateral and anterior columns of the spinal cord, where 
they mingle with the fibres of the posterior longitudinal 
bundle, and with those of the rubro-spinal tract. 
Ultimately they end in the cells of the anterior horiiS. 

(4) The Posterior Longitudinal Bundle, already noticed 
with the fasciculus proprius of the anterior column of 
the spinal cord, and with the dorsal aspect of the 
medulla and pons, is now seen beneath the grey matter 
of the aquaeductus cerebri in near relation to the nuclei 



1 88 THE CENTRAL NERVOUS SYSTEM 

of the 3rd and 4th cranial nerves (fig. 85, page 200). 
We shall afterwards see that it is closely associated 
with the nuclei of the vestibular division of the auditory 
nerve and with the motor nuclei of other cranial nerves, 
co-ordinating the nerves of opposite sides. 

(5) The Spino-thalamic Tract, a part of Gowers' 
tract, joins the fibres of the fillet. It carries sensations 
of touch, of temperature, and of pain from the opposite 
side of the body. 

The Spino-tectal tract, also part of Gowers' tract, is 
similar to the spino-thalamic tract in its origin, in its 
crossing in the spinal cord, and in its course through the 
medulla and pons. It does not, however, like the spino- 
thalamic tract, go to the optic thalamus, but ends in the 
nuclei of the corpora quadrigemina of the mid-brain. 

(6) The Rubro-spinal Tract Monakow's bundle 
prepyramidal tract, starts in the red nucleus of the 
one side, and, crossing the mesial line to the opposite 
side, descends through the lateral part of the pons and 
medulla to the lateral column of the spinal cord, where it 
is found in front of the crossed pyramidal tract. It ends 
in the cells of the anterior cornu. By its means, and 
by means of the brachia conjunctiva, both being, as 
you know, crossed strands, the cerebellum 'of the one 
side is brought in relation with the spinal cord of its 
own side (fig. 79, page 188). 

(7) The descending root of the Uh cranial nerve 
passes through the crura internal to the brachia 
conjunctiva. It ends at the motor nucleus of the 
5th nerve, which lies beneath the upper division of the 
floor of the 4th ventricle. 

(8) The olivary bundle connects the lenticular 
nucleus with the superior olive. 



Fib-res to optic 
t/ialamus and 
cerebral cortex 



FIG. 79. 
Cortico-pontine 



PLATE XXX 

FIG. 80. 
Optic Nerves and Tracts. 

Retina, 



Nucleus 
ruber. 

Prepyramidal 
tract. 




Nucleus (jracilis 
'ucleus cunealu;. 



N - ? Dorso- 

sfrino-cerebella r 

No. 6. Fibres f rum the 
olives. 

No. 4. Fibres from the 
nuci. gracilis 
and runeatiis. 

No. 5. External arci- 
form fibres,. 



tical ceri, 
for sight. 



Sentro-spino- 
cerebellar 



Fasc. of Cell. 
BUrdock. 



^Spino-thalam ic 



FIG. 81. 
Anterior Olfactory Tracts. 



commixs 



Olfactory bulb 
and peaunclt. 



Mitral cells. 



Olfactcn'y 
glomtruli. 



Hippocampus 

major Corpora 

mammillaria. 




Optic thakimus. 
Ntudeus habendvlie. 



Fornix, 
ist. pillars 

Bv/ndle of 
Vicq. d"Aeyr. 



Tegmenit 
ofcerebri. 
pedundf; 



Olfactory 
nerves. 



M* L.jui * duming Edinburgh. 



BRAIN, CRURA CEREBRI 189 

2. Of the Transverse Fibres of the crura cerebri, the 
chief bundles are those which constitute the fasciculus 
of the 3rd and 4th cranial nerves on their way from 
their deep, or subcortical origins, to their superficial 
origins (fig. 54, page 96). 

II. The Crusta, Pes, or Basis the ventral part of 
the peduncles lies in front of the locus niger, and is 
chiefly composed of the pyramidal tracts on their way 
to the medulla. Other strands are, however, super- 
added, for transverse sections of the crusta are much 
larger than those of the pyramids. The following are 
the various tracts of fibres of the crusta : 

(1) The pyramidal tracts motor strands from the 
cortex cerebri occupy the middle and inner part of 
the crusta. They are divisible into two sets an 
external, the pyramidal tracts proper ; and an internal, 
the geniculate fasciculus, which comes from the genu 
of the internal capsule. This genu contains fibres 
connected with the motor part of the 5th, the /th, a^d 
1 2th cranial nerves, and hence with the muscles of masti- 
cation, of the face, and of the tongue (fig. 54, page 96). 

(2) The cortico-pontine tracts pass from the cerebral 
cortex to the nucleus pontis, and then to the opposite 
half of the cerebellum. As they travel through the 
crusta these tracts forms two groups : the one occupies 
the posterior external part of the crusta, and is called 
the fasciculus lateralis, or temporo-pontine tract ; the 
other group mingles with the geniculate and pyramidal 
fibres, and forms the fronto-pontine tract. 

(3) The stratum intermedium, or boundary layer of 
the pes, probably belongs to the pyramidal tracts. 

The relative positions of these tracts to each other 
will be understood by reference to fig. 54, page 96. 



IQO THE CENTRAL NERVOUS SYSTEM 

III. The Substantia Nigra is a semi -lunar band of 
grey matter placed between the two divisions of the 
cerebral peduncles. Slightly convex on its dorsal 
aspect, on its ventral aspect it is denticulated, sending 
processes into the crusta. It is characterised by darkly 
pigmented nerve-cells hence the name. It extends 
through the whole length of the peduncles. Through 
it pass the roots of the 3rd nerve before they emerge 
at the oculomotor groove (fig. 54, page 96). Its con- 
nections and uses are unknown. 

As we have already seen, the two crusfa are quite 
distinct from each other, being separated by the back 
part of the interpeduncular space, called the interped- 
uncular trigone. The two tegmenta, on the other hand, 
are blended together, the median raphe alone indicating 
the line of division. 

The Corpora Quadrigemina (fig. 44 page 72) are 
the four rounded tubercles, separated from each other 
by two grooves, the one longitudinal, the other trans- 
verse. They are placed in pairs, on each side of the 
middle line, below and behind the pineal gland and 
behind the aquasductus cerebri (Sylvius). The anterior 
pair, the larger, are called the colliculi anteriores ; the 
posterior pair, the smaller, the colliculi posteriores. They 
rest upon a thin lamina the lamina quadrigemina 
beneath which runs the cerebral aqueduct (Sylvius). 
Laterally, each pair is prolonged into two white bands 
or cords the anterior and posterior brachia (fig. 59, 
page 114). The anterior or superior brachium passes 
between the pulvinar and the corpus geniculatum 
internum, to the external geniculate body and thence 
to the lateral root of the optic tract. The posterior 
or inferior brachium runs forwards and outwards, 



BRAIN, CRURA, CORPORA QUADRIGEMINA 191 

and disappears beneath the corpus geniculatum 
internum. 

STRUCTURE. The anterior pair of corpora quadri- 
gemina consist of several layers of grey and white 
matter ; the posterior pair, of a central grey core and 
of a white cortex. 

FUNCTIONS. The posterior pair of corpora quad- 
rigemina and the corpora geniculata interna are 
connected with hearing. They both receive fibres 
from the lateral fillet, and in animals with a well 
developed cochlea, the posterior pair of corpora quad- 
rigemina are relatively large. The anterior pair of 
corpora quadrigemina and the corpora geniculata 
externa are connected with sight. 

Homologues of the corpora quadrigemina exist in 
all vertebra. They invariably give origin to the 
optic nerves, and in size bear a direct relation to the 
animal's power of sight. In birds there are only two 
corpora, but they are very large, especially in those 
birds which have great powers of sight. In the mole 
the posterior pair are well developed ; the anterior 
pair are rudimentary. Injury to the optic nerves 
causes the anterior pair to waste, but leaves the 
posterior pair unaltered. 

For the description of the pineal gland and the 
pituitary body see page 161. 

The Aquseductus Cerebri, or aqueduct of Sylvius, 
is the narrow passage between the 3rd and 4th ventricles 
(fig 67, page 152). It is roofed over by a thin lamina 
lamina quadrigemina so called because it supports 
the corpora quadrigemina. Its floor and lateral walls 
are formed by the dorsal part of the cerebral peduncles. 
Internally it is lined by columnar ciliated epithelium, 



192 



THE CENTRAL NERVOUS SYSTEM 



outside which is a thick layer of grey matter the 
stratum griseum continuous with the grey, matter 
locus caeruleus of the 4th ventricle. From this grey 
matter the 3rd and 4th and part of the 5th cranial 
nerves take their origins. 

SUMMARY. The descriptions given in the foregoing 
sections will show us that the cerebrum consists of a 
convoluted cortex ; of basal ganglia ; of four ventricles, 
united by narrow passages; of white strands constituting 
the commissural, projection, and association fibres, and 
of two peduncles with the corpora quadrigemina and 
the aquaeductus cerebri. It might, however, be wise 
to summarize briefly what we have so far learnt, under 
the two following headings: (i) A mesial section of 
the brain ; (2) A general view of the ventricles. 

A mesial section of the brain will show you the 
constituent parts of the three great divisions of the 
brain the fore-brain, the mid-brain, and the hind-brain. 

See fig. 103, page 238, fig. 62, plate xviii., page 130, 
and fig. 67, plate xxi., page 152. 

The fore-brain or prosencephalon comprises the 



Cerebral hemispheres. 

Basal ganglia. 

Corpora geniculata interna. 

Corpora geniculata externa. 

Olfactory lobes. 

Optic nerves and optic tracts. 

Corpus callosum. 



Fornix. 

Lateral ventricles, 1st and 2nd. 

3rd ventricle. 

Tuber cinereum. 

Infundibulum and pituitary 

body. 
Pineal gland. 



Arching through this aspect of the hemisphere you 
will, first of all, recognise the cut surface of the hook- 
shaped corpus callosum, with its genu and rostrum in 
front its splenium behind, and its body between the two. 



BRAIN, SUMMARY MESIAL SECTION 193 

Surrounding the corpus callosum abo/e, in front, and 
behind, are the following sulci and gyri : 
Sulci 

(1) The callosal sulcus which skirts the upper 

border of the corpus callosum. 

(2) The callo so-marginal fissure or sulcus cinguli, 

which runs parallel with the callosal fissure, 
and turns upwards behind as the sub-frontal 
sulcus, the original direction of the fissure 
being prolonged as the sub-parietal sulcus. 

(3) The occipital fissure which forms a deep, 

almost vertical cleft between the parietal 
and occipital lobes. 

(4) The calcarine fissure which runs horizontally 

forwards to join the occipital fissure. 
Gyri 

(i) The gyrus cinguli which encircles the greater 

part of the corpus callosum. 

(2) The marginal convolution lying above the 
sulcus cinguli, parallel with the upper border 
of the hemisphere. 

(3) The quadrate or prcecuneate lobe bounded in 

front by the sub-frontal sulcus, behind by 
the occipital, and below by the sub-parietal 
sulcus. 

(4) The cuneate lobe wedged in between the 

calcarine fissure below and the occipital 
fissure above. 

At the base of the cerebrum, extending between the 
rostrum of the corpus callosum and the crura cerebri, 
you will \ecognise the interpeduncular space, and the 
several structures connected therewith, viz. the posterior 
perforated space, the corpora mammillaria, the tuber 



i 9 4 THE CENTRAL NERVOUS SYSTEM 

cinereum, infundibulum and pituitary body, the optic 
chiasma, and the lamina terminalis. 

Bulging inwards and forming the lateral wall of the 
3rd ventral, is the oval, egg-shaped, mesial surface of 
the optic thalamus, grooved by the sulcus of Monro, 
and marked by the peduncles of the pineal gland, and 
by the remains of the middle commissure. Arching 
beneath the corpus callosum and blended with its 
splenium behind is the body of the fornix, the anterior 
pillars of which descend to the base of the cerebrum 
in front of the optic thalami and the foramina of Monro, 
but behind the anterior commissure and septum lucidum. 
Filling in the racket-shaped interval between the hollow 
of the knee and rostrum of the corpus callosum and the 
pillars and body of the fornix, and united to both, is the 
vertical mesial partition, the septum lucidum, with the 
5th ventricle. If the septum be broken through you 
will expose the fore part of the lateral ventricle and the 
pear-shaped nucleus caudatus of the corpus striatum. 

The mid-brain or mesencephalon comprises the 
crura cerebri, the aqueduct of Sylvius, the lamina 
quadrigemina, and the corpora quadrigemina. 

The hind-brain or rhombencephalon includes 
the cerebellum with the superior peduncles and the 
valve of Vieussens; and the pons and the medulla 
with the corresponding parts of the 4th ventricle. 

The structures forming these two segments of the 
brain can be readily recognised on the face of the 
section. 

(2) Ventricles. A general view Above the level 
of the corpus callosum, the cerebral hemispheres con- 
sist of a solid white core of nerve-fibres, encrusted on 
the surface with a crumpled sheet of grey matter. 



BRAIN, SUMMARY OF VENTRICLES 195 

When, however, the central part or body of the corpus 
callosum has been removed, and when the fornix has 
been cut through where its anterior pillars join the 
body and has, along with the subjacent velum inter- 
positum, been thrown backwards, we expose, near the 
base of the cerebrum, a large centrally situated, four- 
sided space, the corners of which are prolonged into 
six curved recesses, two in front, and four behind. 
Bulging upwards and inwards into this cavity, from 
its side walls, are the four basal ganglia, the pear-shaped 
caudate nuclei in front, and the egg-shaped optic 
thalami behind. By the bulging of these ganglia the 
floor of the space is rendered very uneven, for whereas, 
in the middle line, between the genu of the corpus 
callosum in front, and the posterior commissure behind, 
the space is deep and narrow, at the sides it is shallow 
and wide. 

By the descent of the anterior pillars of the fornix 
to the base of the cerebrum in front of the optic 
thalami, and by the passage, across the middle line, 
in front of these pillars, of the anterior commissure, 
the mesial, narrow, cleft-like interval between the basal 
ganglia is divided into two segments, one anterior, 
between the caudate nuclei, the other posterior, between 
the optic thalami. The latter portion of the cleft, 
that between the optic thalami, is the deepest and 
narrowest part of the entire space. It forms the 3rd 
ventricle, and when the structures which constitute 
its roof are in situ, it is completely cut off from the 
rest of the cavity, the only outlets being through the 
foramina of Monro in front, and through the aqueduct 
of Sylvius behind. For the boundaries of this space 
see 3rd ventricle, page 159. 



196 THE CENTRAL NERVOUS SYSTEM 

On replacing the body of the fornix and the velum 
interpositum, with its choroid plexus and epithelium, 
you will find that the hindermost portion of the space 
or ventricle now exposed is very shallow, for its hori- 
zontal floor and roof almost touch each other, in fact, 
at the back, where the base of the fornix and the 
splenium of the corpus callosum meet, the two are 
blended together. You will also see that the four 
structures, which you have replaced, form not only the 
roof of the 3rd ventricle, but also most of the floor of 
this part of the cavity, the rest of the floor being 
formed by the upper aspect of the optic thalami. 

The floor of the front part of the cavity, that which 
is occupied by the caudate nuclei, is formed, in the 
middle line, where it is deepest, by the rostrum of the 
corpus callosum, at the sides, where it is shallower, by 
the shelving caudate nuclei which are separated from 
the corresponding optic thalami by slight grooves in 
which lie the striae terminales. 

A thin, double, racket- haped vertical, mesial, longi- 
tudinal partition the septum lucidum is' attached 
along the middle line, to both the floor and roof of the 
cavity, the body of the racket filling in the hollow 
between the knee of the corpus callosum and the 
anterior pillars of the fornix, and the gradually tapering 
handle of the racket, filling in the interval between 
the body of the corpus callosum and the body of the 
fornix, until the two meet at the back. By means of 
this two-walled septum, which encloses the 5th ventricle 
between its layers, the cavity is divided into a right 
and a left half, the right and left lateral ventricles, the 
ist and 2nd ventricles, the boundaries of which are 
given on pages 155 and 156. 



BRAIN, CRANIAL NERVES 197 

Of the six curved, horn-shaped recesses which are 
prolonged from the four corners of the space, two turn 
forwards and outwards, one from each corner, into the 
frontal lobes the anterior horns: four are prolonged 
from the posterior corners, two from each, one back- 
wards and inwards into occipital lobes the posterior 
horns : one backwards and outwards then downwards 
and forwards into temporal lobes the lateral horns : 
the boundaries and contents of these horns are given 
on page 157. 

V. ORIGINS OF THE CRANIAL NERVES. 

The Cranial Nerves have each three origins or three 
terminations ; one superficial, one deep or subcorticat and 
one cortical. 

By the term superficial origin or termination 
we mean the points at which the several nerves are 
attached to the surface of the brain ; their deep or 
sub-cortical origins or terminations are the several deep- 
seated nuclei with which they are connected ; their 
cortical origins or terminations are the centres in the 
cerebral cortex to or from which they can be ultimately 
traced. 

i. The Olfactory Nerves ist pair. On page 141 
it was stated that the olfactory brain consisted of two 
divisions an anterior, the olfactory lobe ; and a 
posterior, the limbic lobe. 

(i) The OLFACTORY LOBE comprises 
(a) The olfactory bulb and its peduncle. 
(/^) The anterior perforated spots. 

(c] The olfactory area of Broca. 

(d) The olfactory trigone and tubercle. 



i 9 8 THE CENTRAL NERVOUS SYSTEM 

(e) The peduncles of the corpus callosum or sub- 
callosal gyrus. 

(a) The OLFACTOKY BULB and its peduncle, origin- 
ally hollow outgrowths of the fore-brain, form a 
club-shaped body with the head of the club in front, 
and the handle of the club behind. They occupy the 
olfactory grooves on the under aspects of the frontal 
lobes. 

The bulb or head of the club is oval in shape and 
reddish in colour. It receives, through the cribriform 
plate of the ethmoid, about twenty fine non-medullated 
nerve-filaments, which come from the nerve-cells of the 
olfactory mucous membrane. These filaments end in 
brushlets of branches in the glomeruli of the olfactory 
bulbs, these cells being their first or primary peripheral 
sub-cortical centres. From these glomeruli new fibres 
take their origin, and by means of the mitral cells, their 
second sub-cortical centres, become connected with the 
fibres of the olfactory peduncles. 

The OLFACTORY PEDUNCLES or tracts, the handles 
of the clubs, are prismatic bands of nerve-fibres which 
occupy the hinder portion of the olfactory grooves. 
Widening out behind, each peduncle divides into two 
roots or limbs, an outer or lateral, and an inner or 
mesial. The lateral root passes backwards towards the 
fissure of Sylvius to (b] the anterior perforated spot, 
where some of the fibres efid, while others pass through 
the space to the uncinate gyrus, the cortical centre for 
smell, at the tip of the temporal lobe. The mesial root 
runs inwards towards the great longitudinal fissure. 
Most of the fibres of this root end in (c) the olfactory 
area of Broca which lies anterior and internal to the 
mesial limb of the olfactory peduncle. Other fibres go 



BRAIN, CRANIAL NERVES 199 

to (d) the subcallosal gyrus or peduncle of the corpus 
callosum. (e) The small conical elevation, the olfactory 
trigone or tubercle which occupies the interval between 
the two roots, and to which some of the fibres of the 
peduncle can be traced, is often regarded as a third 
root. Through these several roots the olfactory peduncle 
connects together the two ends of the limbic lobes. 

(2) For the LIMBIC LOBE see pages 139 and 141. 
For the central connections of the olfactory system see 
fig. 81, page 1 88. 

The Cortical Centres for smell are the uncinate gyrus 
of the same side, and through the anterior commissure 
the uncinate gyrus of the opposite side (fig. 42, 
page 64). 

It is worthy of note that in animals with well- 
developed organs of smell the gyrus hippocampi, the 
striae longitudinales, and the fascia dentata are well 
marked ; whereas in man, with small olfactory lobes, 
they are relatively small. Injury to the olfactory bulb 
causes atrophy of the uncinate gyrus, on the other 
hand, gross lesions of the gyrus cause disorders of the 
sense of smell. 

2. The Optic Nerves 2nd pair can be traced 
from the eyeballs through the optic foramina to the 
mesial band the optic commissure or chiasma, in 
which they partially decussate (fig. 80, page 188. 
From this commissure the optic nerves run backwards, 
as the optic tracts, round the outer sides of the crura 
cerebri, and then bifurcate into two limbs, an internal 
limb wnich goes to the CORPORA GENICULATA INTERNA, 
and an external limb, one part of which can be traced 
to the CORPORA GENICULATA EXTERNA, the Other to 
the FULVINAR of the optic thalamus and to the 



200 THE CENTRAL NERVOUS SYSTEM 

COLLICULI ANTERIORES or anterior pair of the corpora 
quadrigemina (fig. 59, page 1 14, and fig. 80, 'page 188), 
These ganglia are the sub-cortical centres for sight, and 
they degenerate when the eye of a young animal is 
destroyed. 

In the optic chiasma and tracts there are three 
sets of fibres (i) an outer set, the direct fasciculus, 
which lies on the outer side of the chiasma and 
tract, and which comes from the macula lutea and 
from temporal half of the corresponding retina; (2) a 
mesial set, the crossed fasciculus, which comes from the 
nasal half of the corresponding retina and decussates 
with the fibres of the opposite side, so that those of 
the right eye reach the left tract, and those of the 
left eye the right tract. (3) The internal set, which 
passes from one tract to the other and then back to 
the brain without entering the eye, is known as the 
commissure of Gudden. It connects together the 
corpora geniculate of the one side with the colliculi 
posteriores of the other. It has nothing to do with 
sight, for the roots of the optic tracts, which we 
traced to the corpora geniculata interna, do not, like 
the other roots, undergo atrophy, when the eyes are 
destroyed. 

Besides afferent or visual fibres, the optic nerves 
also contain others affecting papillary reflexes. 

The Cortical Centres for sight are situated in the 
occipital lobes, in its cuneate and lingual lobes, and in 
the outer aspect of the occipital pole (figs 39 and 42, 
page 64; fig. 62, page 130). They are connected with 
the sub-cortical centres by means of a bundle of fibres, 
the optic radiation, which contains both afferent 
and efferent fibres, and which passes between these 



Kiu. 82 Pedunculi cerebri 




PLATE XXXI 
FIG. 83 



rTyL Aquteductus 
\f cerebri 



cerebri 

Nucleus of 

3rd nerve 



Nucleus o, 
4th nerve 



3rrf nerve 




Ant. 



Post. 



collicul 



1th nerve 

Brachia 
conjunctiva 



Valve 

of 
Vieussens 



Corpora 
quadrigemina 

-^ 

Aqutzductus 
cerebri 

Nuclei of 
3rd nerve 



Zrd nerve 



FIG. 84 



Nucleus of 
6th nerve . 




Sensory 

nucleus 

5th nerve 



FIG. 85 
Section of pans 



Post. long, 
bundle 



FIG. 86 
Fourth Ventricle 




Sensory nuc. 
of 5th nerve 



Sensory 
div. of/ 
Motor 5* h. n.' 




Motor div 
of 5th n. 

\ Motor 

\nuc. of 
5th n. 



Spinal 
root of 
5th n. 



Pyramidal 
tracts 






FIG. 87. 



FIG. 88 



Restiform 
body 



8M 



1th nerve 




. ofQth neive. 
Nuc. of 1th nerve. 



PLATE XXXII. 



Nucleus of 
3rd nerve 



Fillet. 



f^- : ~_- Mesial raphe'. 

___J|fc_^-<_ Pyramids. 

piC-T^^ ^ 



?,rd nerve 



1th nerve 




Nucleus 
f>f 12th n. 



6<A nerve; 



Nuc. of Bechterev}. 



Deitery'' nucl. 
Nuc. of 
desc roo 



FIG. 90. 



FIG. 89. 

^Principal auditory 

nucleus. External 

rectus. 




Viet. 



Qth 



A Fibres to cerebellum. 

B. Fibres t 

\ rpost. long, bundle. 

2 I nuc. of 3rrf and Qth nerves. 

3 / cotticuli poster. 

4 corpora geniculata inter. 

5 ^temporal cortex. 
Fasciculus 



Superior 

olive. 
Corpus 
trapetoid 

Pyramids. 




soUtariwi. 

Restifvnn 
body. 



9th nerve.- 



Olivary^ - 
body. 







\2th nerve. 



FiG. 91. 

Nucl. of 

12/A nerve. 

.-Nucl. 
ambiguus. 



* Pyramids. 



FIG. 92. Nucl. of Vagus 
IQth nerve. 



IQtk nerve. 




Infer, 

Accessary 
olive. 



BRAIN, CRANIAL NERVES 201 

sub-cortical centres through the sub-lenticular portions 
of the internal capsule. 

From fig. 62, page 130 you will see that the calcarine 
fissure divides the hemicentre for sight into an upper 
and a lower division. Damage done above the 
calcarine fissure, i.e. in the cuneate lobes, causes blind- 
ness in the upper quadrant of the retina, but in the lower 
quadrant of the field of vision ; whereas, on the other 
hand, damage below the calcarine fissure i.e. in the 
lingual lobe will cause loss of vision in the lower 
quadrant of the retina, and therefore in the upper 
quadrant of the field of vision. 

The centres for sight are connected with the centre 
for articulate language in the frontal lobe ; with the 
auditory centre in the temporal lobe ; and with the 
centre for visual memory in the angular gyrus of the 
parietal lobe. 

The 3rd Nerves (figs. 82, 83, 84, page 200) spring 
from the fore part of a longitudinal column of cells, 
on each side of the middle line, in the grey matter of 
the FLOOR of the AQUyEDUCTUS CEREBERI (Sylvius) 
(fig. 50, page go, and figs. 83, 84, page 200). This 
collection of cells is called the oculomotor nucleus. It 
lies beneath the anterior pair of corpora quadrigemina, 
and is a continuation of the grey matter of the anterior 
horn of the spinal cord. Traced from the cells of this 
nucleus the deep or sub -cortical origin the fibres of the 
3rd nerves pass through the posterior longitudinal 
bundle, through the red nucleus, and through the 
locus niger (fig. 82, page 200), to the oculomotor 
groove their superficial origin on the inner side of- 
the cerebral peduncles, close to the upper border of 
the pons. 



202 THE CENTRAL NERVOUS SYSTEM 

The nuclei of the 3rd nerves are closely connected 
with the nuclei of the 4th and 6th nerves, the nucleus 
of the 6th nerve of the one side being united, by means 
of the posterior longitudinal bundle, with the nucleus 
of the opposite 3rd nerve (fig. 84, page 200). . There 
is probably a partial decussation of the fibres of the 3rd 
nerve, these decussating fibres supplying the opposite 
internal rectus. 

The nucleus of the 3rd nerve gives rise to two sets 
of fibres : 

(1) Those to the voluntary part of the levator 
pilpebrae superioris and to the. extrinsic muscles of the 
eyeball, except the external rectus and the superior 
oblique. The involuntary part of the levator palpebrae 
is supplied by the sympathetic ; the superior oblique 
by the 4th nerve ; and the external rectus by the 
6th nerve. 

(2) Those to the intrinsic muscles of the eyeball, viz. 
the sphincter pupillae, and the ciliary muscle. This 
connection, however,- is not a direct one, but through 
the lenticular ganglion and the short ciliary nerves, for 
this ganglion, which belongs to the cranial autonomic 
system, is the peripheral motor nucleus which presides 
over the sphincter pupillae. 

The following are the symptoms associated with 
paralysis of the 3rd nerve : 

(i) Drooping of th~ upper eyelid; (2) external 
squint, the eyeball being turned down and out; (3) 
double vision ; (4) loss of the power of accommodation ; 
(5) dilation of the pupil : (6) chromatic and spherical 
aberration ; (7) erroneous projection ; (8) a tendency 
for the tears to flow over the cheek. 



BRAIN, CRANIAL NERVES 
TABLE OF THE NUCLEI OF THE THIRD NERVE. 



203 





r i. A mesial set," 






to the ciliary 
muscle 


Through the len- 




' I. A Superficial 
Group 


2. A lateral 


ticular ganglion 
and short ciliary 






set, to the 










nerves. 






s phin c t e r 




Nuclei of 




k pupillae 




the 3rd- 
Nerve 




f to internal rectus. 
r 1.- A mesial set 4 . , . 
\. to inferior rectus. 




II. A Deep 
Group 




to voluntary part of 
the levator palpe- 






bras superior. 




^ 2. A lateral set . 


to the superior 




rectus. 




to the inferior 




oblique. 



The 4th Nerves will be seen on the outside of 
the pedunculi cerebri, between the cerebrum and the 
cerebellum, (fig. 66, page 148). They are small, long, 
and slender, and arise from a NUCLEUS deep or sub- 
cortical origin. in the wall of the AQU^DUCTUS CEREBRI 
(Sylvius), behind that of the 3rd nerve and beneath the 
colliculi posteriores (fig. 83, page 200). After leaving 
their nuclei of origin, the fourth nerves pass back- 
wards and outwards through the crura cerebri, then 
backwards and inwards to the SUPERIOR MEDULLARY 
VELUM the superficial origin where they decussate, 
so that the left nerve comes from the right nucleus, 
and vice versa (fig. 83, page 200). Hence it follows that 
the right 4th nerve supplies the left superior oblique. 

The fourth nerve is connected with the nucleus of 
the sixth nerve of the opposite side. 



204 THE CENTRAL NERVOUS SYSTEM 

The 5th Nerves, which are composite nerves, being 
partly sensory and partly motor, take their superficial 
origin from the sides of the pons, near its upper margin. 
They arise by two roots, the one large, sensory 
ganglionic t the other small, motor aganglionic (fig. 
66, page 148). The small MOTOR ROOT is the higher 
of the two, and is separated from the larger root by 
some of the transverse fibres of the pons. The deep or 
sub-cortical origin of this smaller or motor root is the 
MOTOR NUCLEUS lying just above the LATERAL ANGLE 
of the 4TH VENTRICLE, in that division of the floor of v 
the 4th ventricle that is formed by the back of the 
pons (fig. 50, page 90). It is joined, from the mid-brain, 
by the superior or descending root of the 5th nerve, 
which comes from the accessory nucleus a column 
of grey matter at the outer side of the grey matter of 
the aquaeductus cerebri (Sylvius) (fig. 50, page 90). 
From this, its deep otigin, the two parts of the motor 
root of the 5th nerve pass forwards and outwards to 
their superficial origin between the PONS and the 
BRACHIUM PONTIS. 

The large SENSORY ROOT has its nucleus of 
origin in the Gasserian ganglion, situated on the front 
of the apex of the petrous part of the temporal bone. 
The unipolar nerve-cells of this ganglion give off two 
branches, one of which passes into the peripheral nerve, 
the other enters the pons, and there divides into 
ascending and descending branches. The ascending 
branches end amongst the cells sub-cortical termina- 
tionforming the sensory nucleus of the 5th nerve. 
This nucleus lies under cover of the overhanging lateral 
wall of the pontine part of the 4th ventricle, beneath 
but close to the outer side of the motor nucleus (fig. 50 



BRAIN, CRANIAL NERVES 205 

page 90 ; fig. 85, page 200). The descending branches 
form the spinal, descending or inferior root of the 5th 
nerve. This root can be traced down the spinal cord 4 
as far as the second cervical nerve. It lies to the outer 
side of the substantia gelatinosa of Rolando, the cells 
of which constitute the spinal nuclear tract of the 5th 
nerve (fig. 86, page 200). 

The 6th Nerves take their superficial origin near 
the middle line from the groove between the upper end 
of the anterior pyramids of the medulla and the lower 
border of the pons Varolii (fig. 66, page 148). Their 
deep origin is situated underneath the outer part of the 
FASCICULUS or EMINENTIA TERES in the fore part of 
the floor of the 4th ventricle, in front of the striae 
acusticae or medullares (fig. 50. page 90). From this 
origin the nerve-bundles run forwards and outwards 
through the thickness of the pons to their superficial 
origin. The nucleus of the 6th nerve may be connected, 
by means of the posterior longitudinal bundle, with the 
3rd nerve of the opposite side (fig. 84, page 200, and 
fig- 9> P a e 200). This connection is probably an 
indirect one through the nucleus of the opposite 3rd 
nerve, for there are no fibres directly from the 6th 
to the 3rd nerve. 

Though the 3rd, the 4th, and the 6th nerves are 
mainly motor nerves, they also contain afferent fibres 
which keep up the tone of the ocular muscle. 

The 7th Nerve consists of two parts the FACIAL 
or portio dura, and the PARS INTERMEDIA. The FACIAL 
the 7th nerve takes its superficial origin at the 
lower border of the pons, from the groove between 
the upper ends of the olivary and restiform bodies 
(fig. 66, page 148). Its deep or sub-cortical origin is the 



206 THE CENTRAL NERVOUS SYSTEM 

facial nucleus in the formatio recticularis of the dorsal 
aspect of the pons, near the nucleus of the 6th nerve, 
but external and deeper in beneath the floor of the 
4th ventricle (figs. 87, 88, page 200). This nucleus 
extends from the region of the nucleus of the 3rd 
nerve above, to the nucleus of the I2th nerve below. 
On leaving the nerve-cells of the nucleus, the fibres of 
the facial nerve are, at first, directed backwards and 
inwards towards the middle line, internal to the 
nucleus of the 6th nerve. They then ascend for a 
short distance, behind the nucleus of the 6th nerve, 
close to the floor of the 4th ventricle, forming part of 
the eminentia teres. Bending downwards and outwards 
over the upper end of the nucleus of the 6th nerve 
(fig. 87, page 200), the facial nerves now run forwards, 
outwards, and downwards to their superficial origin 
at the lower border of the pons 

The facial nerve supplies all the muscles of ex- 
pression, but the corrugator supercilii and orbicularis 
palpebrarum are supplied by fibres from the upper 
cells of this nucleus those near the nucleus of 
the 3rd nerve; and the orbicularis oris by fibres from 
the lower set of cells those near the nucleus of the 
hypoglossal nerve. Some authors hold that these 
muscles are supplied from the nuclei of the 3rd and 
1 2th nerves respectively (fig. 88, page 200), for, in the 
pons, the facial nerve is joined, through the posterior 
longitudinal bundle, by fibres from the nuclei of the 3rd 
and the I2th nerves. 

The PARS INTERMEDIA the so-called sensory root 
of the facial nerve is a small bundle of nerve-fibres 
which lies between the facial and auditory nerves, and 
is connected with both. It carries taste-fibres to the 



BRAIN, CRANIAL NERVES 207 

glosso-pharyngeal nucleus. As you no doubt already 
know, the cells of the geniculate ganglion of the facial 
nerve have, as usual, a central and a peripheral set of 
processes. The central processes form the pars inter- 
media of the facial nerve ; the peripheral processes 
constitute the chorda tympani nerve. This nerve the 
chorda tympani starting in the taste bulbs of the 
anterior two-thirds of the tongue, at first travels with 
the lingual branch of the third division of the 5th nerve, 
but afterwards joins the facial nerve in the aquaeductus 
Fallopii, and thus reaches the geniculate ganglion of the 
facial nerve. From the cells of this ganglion the taste- 
fibres are conducted, through the pars intermedia of the 
facial, to the fasciculus solitarius and to the nucleus of 
the glosso-pharyngeal nerve. There is, however, another 
possible route for the taste-fibres, viz. through the 
chorda tympani to the geniculate ganglion, thence 
through the great superficial petrosal nerve to Meckel's 
ganglion, and through its spheno-palatine branches to 
the superior maxillary division of the 5th nerve. Finally 
through the Gasserian ganglion and the trunk of the 
5th nerve they reach the cortical taste-centres in the 
tip of the temporal lobe. 

The Auditory Nerve the 8th Nerve. Though 
apparently a single nerve, it is made up of two distinct 
nerves, corresponding with the two divisions of the ear, 
the cochlea, through which we hear, and the vestibule 
and semi-circular canals, which are concerned with the 
maintenance of equilibrium. The auditory nerve takes its 
superficial attachment to the brain in the same groove 
with, but behind, the facial nerve, from which it is 
separated by the pars intermedia (fig. 66, page 148). Its 
superficial origins, as with all sensory nerves, are the 



208 THE CENTRAL NERVOUS SYSTEM 

ganglia vestibular and spiral on the course ot the 
nerve. Traced from the cells of these ganglia the 
central or axis-cylinder processes enter the medulla, 
and divide into ascending and descending branches, 
which end in tufts at the sub-cortical or deep termina- 
tion of the nerve. 

The auditory nerve has two roots a mesial and a 
lateral root, corresponding with its two divisions, vesti- 
bular and cochlear (fig. 89, page 200). 

(D The mesial root VESTIBULAR DIVISION - 
the anterior, ventral, or upper root is formed, as we 
have just seen, by the central processes of the bipolar 
nerve-cells of the vestibular ganglion ganglion of Scarpa 
found on the auditory nerve within the internal auditory 
meatus. Passing backwards through the substance of 
the medulla and pons, internal to the restiform body (fig. 
89, page 200), the fibres of this root divide into ascending 
and descending branches. The former or ascending 
branches end in the cells of the (i) VESTIBULAR NUCLEUS 
the dorsal vestibular or principal vestibular nucleus 
which lies beneath the AREA ACUSTICA trigonum 
acusticum of the 4th ventricle (fig. 50, page 90). By 
means of collaterals some of the fibres are united to 
the two contiguous nuclei (2) of Deiters and Bechterew 
(fig. 89, page 200) ; while others (3) pass by these 
nuclei and go directly to the cerebellum. The descend- 
ing branches of this division form the descending root 
of the vestibular nerve, which ends in the spinal 
NUCLEUS of the VESTIBULAR root, though some of the 
branches, along with fibres from the nucleus of Deiters, 
can be traced through the medulla to the spinal cord, 
as the vestibular spinal tract (Lowenthal): Other fibres 
from the nuclei of Deiters and Bechterew go to the 



BRAIN, CRANIAL NERVES 209 

nuclei fastigii of the opposite half of the cerebellum ; 
to the corpus dentatum, and to the cortex of the 
vermis cerebelli ; others join the posterior longitudinal 
bundle, and, through it, reach the nucleus of the 6th 
nerve of the same side, and the nuclei of the 3rd, 4th 
nerves and the motor nucleus of the 5th nerve of the 
opposite side. 

The vestibular root carries impulses from the semi- 
circular canals, and is concerned with the maintenance 
of equilibrium, and not with hearing. It is connected 
with the optic thalamus, the centre for sight, hence 
the explanation of the fact that when we hear a 
sudden sound the head is turned to the direction from 
which it" comes. 

(2) The lateral root COCHLKAR DIVISION lower 
or posterior root is the true nerve of hearing, for it 
alone is connected with the organ of Corti. It arises 
as the central processes of the bipolar nerve-cells in 
the coiled spiral ganglion of the lamina spiralis of the 
cochlea. Passing backwards into the medulla, on the 
outer side of the restiform body, as the lateral cochlear 
root lower or posterior root of the auditory nerve, 
its fibres divide into ascending and descending branches. 
The ascending branches end in the cells of the VENTRAL 
COCHLEAR NUCLEUS accessory cochlear nucleus 
placed in front of the restiform body, between the 
mesial and lateral roots of the auditory nerve (fig. 89, 
page 200). The descending branches end in the DORSAL 
COCHLEAR NUCLEUS a collection of cells amidst the 
fibres of the lateral root as they wind round the outer 
side of the restiform body (fig. 89, page 200). This 
nucleus will be found beneath the TUBERCULUM 
ACUSTICUM the elevation ot the trigonum acusticum 

p 



210 THE CENTRAL NERVOUS SYSTEM 

beneath the striae medullares, close to the lateral recess 
of the 4th ventricle (fig. 44. page 72). 

The Central Connections of the cochlear or lateral 
division of the auditory nerve are as follow (fig. 89, 
page 200): (i) from the ventral or accessory nucleus 
through the corpus trapezoideum, and (2) from the 
dorsal or lateral nucleus through both the striae medul- 
lares and corpus trapezoideum, fibres travel to both 
superior olives, to the lateral fillet of the same side, 
but mostly of the opposite side, to the posterior pair 
of corpora quadrigemina, and to the corpora geniculata 
interna. Finally, through the sub-lenticular part of the 
internal capsule, the auditory fibres, auditory radiation, 
reach the CORTICAL CENTRES for hearing, situated in the 
SUPERIORTEMPORALconvolution.and in the TRANSVERSE 
TEMPORAL gyri, a group of convolutions on the upper 
aspect of the temporal lobe, within the fissure of 
Sylvius. 

These cortical centres receive impulses from both 
ears, but mainly from the one of the opposite side. 

As the connections of the divisions of the auditory 
nerve are somewhat complex they are given in the 
table, on pages 213 and 214. 

The Glosso-pharyngeal the Qth cranial nerve- 
has two parts : a motor, and a sensory. The motor 
part of this nerve takes its deep or subcortical origin 
from the NUCLEUS AMBIGUUS or accessory vagal 
nucleus (fig. 50, page 90, and fig. 91, page 200). The 
sensory part starts in the ganglia on the nerve the 
petrous and jugular ganglia. On entering the medulla 
its fibres divide into descending branches, which join 
the fasciculus solitarius ; and ascending branches, 
which end in a special nucleus, common to this nerve 



BRAIN, CRANIAL NERVES 211 

and to the vagus. This nucleus lies beneath the inferior 
fovea and ala cinerea of the lower half of the floor of 
the 4th ventricle (fig. 44, page 72). The superficial 
origin of the glosso-pharyngeal nerve is the groove 
between the olivary and restiform bodies (fig. 66, page 
148). The glosso-pharyngeal nerve is probably a pure 
sensory nerve, its motor fibres being derived from the 
spinal accessory nerve. 

The Vagus the loth cranial nerve is partly motor 
and partly sensory. The motor portion of this nerve 
springs from the nucleus ambiguus or accessory vagal 
nucleus of the same and of the opposite sides (fig. 92 
page 200). The sensory fibres arise in the bipolar cells 
of the ganglia of the root and of the trunk of the vagus, 
and after entering the medulla divide into descending 
branches, which join the fasciculus solitarius, and ascend- 
ing branches, which end in tufts in the vagal nucleus 
beneath the ala cinerea (fig. 92, page 200). The super- 
ficial origin or termination of this nerve is the groove 
behind the olive. 

The Spinal Accessory the nth cranial nerve- 
is a pure motor nerve. It has two parts : a spinal 
part, and an accessory part. 

(1) The spinal part takes its superficial origin from 
the spinal cord behind the anterior roots of the upper 
five spinal nerves. Its deep or subcortical origin is the 
column of cells in the spinal cord the dorso-lateral 
group which extends from the olive as far down as 
the 5th cervical nerve. 

(2) The accessory or bulbar part has superficial and 
deep origins very similar to those of the vagus, viz. \. 
in the one case, from the groove behind the olive ; in 
the other, from the nucleus ambiguus, and from the 



212 THE CENTRAL NERVOUS SYSTEM. 

column of cells lying beneath the ala cinerea of the 
4th ventricle (fig. 44, page 72). This column of cells 
is common to the glosso-pharyngeal, to the vagus, 
and to the bulbar part of the spinal accessory. This 
bulbar portion of the spinal accessory nerve should 
really be regarded as part of the vagus, and not as a 
separate nerve. 

The Hypogflossal I2th nerve takes its superficial 
origin by several filaments from the groove between the 
anterior pyramids and the olives (fig. 66, page 148). 
Its deep origin is a column of cells lying near the middle 
line, close to the surface of the lower half of the 
floor of the 4th ventricle, beneath the lower part of 
the fasciculus teres. This area is often called the 
TRIGONUM HYPOGLOSSI (figs. 50, 51, page 90, and fig. 
91, page 200). From its cells the fibres of the nerve 
can be traced through the formatio reticularis to its 
superficial origin. 

It is worthy of note that, just as in the spinal cord, 
the motor tracts and the motor nerves and their nuclei 
are anterior, and the sensory nerves posterior, so also 
do the motor faculties occupy the anterior and the 
sensory the posterior part of the brain. 



BRAIN, AUDITORY NERVE 



213 









rt 


4) *S.rtS5**<J 








C 


3C. rt 2 4> D. ^"C 






(/) 

OJ . 
"71 1/1 


Is 


</1(:i 'o_-Q N "^ 1 "'rt<u 






U 3 

C^ 


$ 


"So^SS^.-^^o-o 






C ~ 


rt c 


3 "73 C? w ~* ^5 "" "* ^* CL. 






>^ 3 


3 - 


oX^^*^2^^ S" 






8 c 


^rt 


4= 






% "rt 

W 


25 

i.3 




rt -^ 






o <- 










ca _rt 

b 


C 
y u 

u be 


fS "O" J_ r Q 


w 



z: 

a 


rt 

_c 

_rt 


2*3 

<- ) 


rt 

S3 o 

ts 


Q 3 2 en C u - y 

5.H g - 2-5 > 

nr c <oj3 <"-rt~ 


PS 




D O 





tj C v "" f} ^ o 


a 

h 


V 

1 


^JS 


0.8 


o o S 


W 










^ 


"3 






1/1 '5 2' ' -^ " ^ ti 


^ 


rt 






> *7j 1> ^ 3 Q "" *i 'O 


o 


* " 






* " 3 T3 '"^ C j^ ,0 " J/} 


s, 


bo 






O c "" ^* i-. r? 




C 


, 




^ " 4J 


w 


rt 


rt 


rt 


O "^** -rt <"{ ^1* *^ ** { i ^^ .^ 




CO 


O 


O 


"C 5 "" X ^"S ^ *J fE^ ^ 


tf 


-3 tn 


^ rt 


'5 rt 


4) 8 S ^* - TJ^O 


w 


rt .^ 

'2kb 

V o 


8 "bo 

u ^5 C 
D 3 rt 

^ </i bo 


^ S'-So 

c - r) 5 

00 3 =? 

oo bo 


S 


2 


5 


_O 


J3 


Jo g | 











"^ *^ TO CU ^ 


3 








-5.^r "C g a; "XJ 


s 








> ^"i ^ / , *"rt C *^ M S 


* 








cboaj .c-^Ca'S ..3JJ 


h 
C 


rt 


.5 




8-^."H bocqrta.g -^ a >. 

rt yj 2 ^ ^O 3 C G 


TABLE 


"bo 

c 


gS 


"bo 

rt 

bo 

"rt 
o 




2^4; i-rt O*O O<->-.O 

a ="^ r , i 5 , 
| S | ~~^ rt' 

4-t 1> Q tO C/3 4-* (/) 

u CO w u D C 3 




1) '5 


, _ 




Q D O 4) m V 


.1 
.5 


II 


S 

<- o 

C J3 




*> "" C! S 3 E 3 

3" rt O C O q 


*<sk 


Cu c/3 


Uco 




c/} i: ,. ^ ^ 


(5 








rt c 


^ 











-1 




S.5 




y C y 


s^- 




. 1 




- rt 


^ 




H c 




o a 


>J 




u rt 




U o 







214 



THE CENTRAL NERVOUS SYSTEM 



!si 


"3 


c D " hi 
C > O O 


3 


rt 
C 


tn 

OJ 

E 





cB i- o in 
<n 4; "^ in 
**- C '+- V. 


CL 


'EL 

If! 




rt 


j- U 


<a 


_o 


V- 


be 


<u *ij c/i rt 


"*"* 


"3 


O 


g 


> Tf . V 


a 




J3 


"o 


S c|| 1 


c 
ed 


<S1 

V 




C- 0) 


(-; TO Q^ 


tn 


^ 


.0 




^ T3 Sj= 


3 


i 




o 


v^ r-Vin tri " 


s 




S rt > 

S V 


in Q., 
3 O. 
4> O 


o .^ o ^ 

<" . o! i 2 
3 t) - o - 0) 3 


:| 


o 

<J 


5 E 13 


(J >*; 

3 


"o -^ "u "o "o Is T3 


2 O 


13 
c 


1 S o 


C ^5 
H *U . V 


3333 
C C C C 


a, 


'a. 

in 


V S "O 
'5 

W 3 in 


rt o ,0 
"5 4) - O 

_5 h. Z3 ~ 


13 




^0 


O rt 3 


'Z; u o rt .^ 


c 


(/) 


C 


Y NERVE FOR REFEREN 

bular ganglia in internal 
rincipal auditory nucle 


vestibular nucleus, 
erior vestibular nucleus, 
istibular root spinal ves 
nucleus. 

(to nuclei fastigii or tecti 
to corpus dentatum cere 
to cortex cerebelli later 
v to cortex vermis cerebell 


Is 

Ij 

- C rt 



to fillet and through il 
cortex of the opposite 


o 

o 
'C 

u 

c 
tn . 

~ 


g |f 


15 " > 


c 






H > 4, 


H "* bo o u 


rt ^ 

3 






g o 3. 


""c 3. "5 


si 

W CJ 

^^ r5 




11 


^3 ^ JJ.J V) <U CS ^ 


u ^ 
3 c 
^C ^ 




H 


(i 


QJ D " w . T^ Q 2 


13 <U 




1/1 


t^ r/> L_. ^ 


i"**! CQ ^ rt 


fist; 




u rt 


^ t* O ^ 


. ,, *^; C '5 


'G <o 




a; a 


< .f "o 1 o o w . *o 


cQ 




'S 


H -S .5 3 -1 


: 3 3 3 jj fi'5 


Ra 




n-S 


*> b/3 ^_i ( 
^ g 3 : 


"333^ g 


i- s 




I s 


^ bo c 


c c c c:- 


* 




"*" _, 


> rt 

^ .y 


13 


u 






C rt ; rt 


'tE 55 


13 '5 is. a 






^ 4J O "TJ. 


2 O "T^. 


O ' U 






1 T 3 S* 


I il 


_e c & 'O ti c 

"tj. D 3 C O W 






J: *3 < < 


j (J in bo 


. O i/) rt cj oo 






S (X 


J 


|Xj 







BRAIN, GENERAL SUMMARY 215 

GENERAL SUMMARY. 

Having in the preceding sections described the 
several parts of the brain and spinal cord, we shall 
now take a general survey of both the grey and white 
matter of the whole Central Nervous System. 

Grey Matter. The grey matter of the cerebro- 
spinal nervous system consists of a countless number 
of superimposed neurones, with their dendrones or 
protoplasmic processes, and their axones or axis-cylinder 
processes. The former are centripetal, carrying im- 
pulses towards the cells; the latter are centifrugal, 
carrying impulses away from the cells. By means of 
these two sets of processes the different parts of the 
nerve-axis are brought into relation with each other, 
and with every other part of the body. The neurones, 
though, according to some authorities united with each 
other by delicate neuro-fribillae, may for all practical 
purposes be regarded as independent elements, their 
processes being contiguous only and not continuous. 
The cell bodies, supported by neuroglia and mainly 
nutritive in function, constitute the grey matter : their 
processes, especially their axis-cylinder processes, form 
the various white strands. 

A. In the CEREBRUM the grey matter forms the 
cortical and the sub-cortical ganglia, the former covering 
the surface, the latter lying in the interior. 

I. The CORTICAL GANGLIA CORTEX CEREBRI can 
be mapped out into certain areas, which in many cases 
overlap each other, and which, for want of better 
names, are called the motor, the sensory, and the 
association areas. The cortical motor areas carry out 
the movements initiated by the will, the cortical 
sensory areas are responsible for the appreciation of 



216 THE CENTRAL NERVOUS SYSTEM 

space relationships and for the recognition of likeness 
and differences. Of the association areas we know little 
or nothing. 

(1) The MOTOR AREAS are said to occupy the 
anterior central gyrus ascending frontal convolution. 
They include both the superficial and deep part of 
this gyrus, viz. that part which forms the anterior 
wall of the fissure of Rolando. They also extend into 
the paracentral lobe on the mesial aspect of the 
hemisphere. 

(2) The SENSORIAL AREAS are not so well defined 
as are the motor areas. 

(a) The centres for common sensibility probably 
reside in the post -central gyrus or ascending parietal 
convolution and have quite a different structure from 
the anterior central gyrus (see page 147). Some sensory 
fibres also go to the anterior central convolution, hence 
the" name, sensory-motor areas, sometimes applied to 
these convolutions ; others are supposed to end in the 
contiguous convolutions of the parietal lobe. 

(b) The centres for sight are found in the cuneate 
lobe and in the outer aspect of the occipital pole (fig. 
28, page 50). The centre for visual memory is located 
in the angular gyrus of the parietal lobe (fig. 28, 
page 50). 

(c) The centres for the sense of smell and of taste 
are placed in the hippocampal and uncinate gyri, on 
the inner aspect of the hemisphere (fig. 42, page 64). 

(d} The centres for the sense of hearing reside in 
the upper temporal gyrus, and in the upper surface of 
the temporal lobe, that surface within the fissure of 
Sylvius. 

(e} The centres for the stereognostic sense are 



BRAIN, GENERAL SUMMARY 217 

located in the superior partietal lobule, but it is very 
doubtful whether this is a primary sensation or merely 
a complex of several sensations. 

(3) The ASSOCIATION AREAS constitute two-thirds 
of the entire cerebral cortex, occupying most of the 
frontal, temporal, parietal, and occipital lobes. They 
cannot be stimulated from without. 

2. The SUB-CORTICAL or BASAL GANGLIA, VIZ. the 
corpora striata and the optic thalami, are found in 
the interior of the cerebral hemispheres. The optic 
thalami are connected with sensation ; the corpora 
striata, with motion. The former the optic thalami 
do not, like the cerebral cortex, enable us to differentiate 
and discriminate degrees of sensation, but only apprise 
us of crude and elementary feelings, such as those ot 
heat, of cold, of touch, of pleasure or of pain, without 
recognising their intensities, i.e. distinguishing differences 
of kind, but not differences of degree. 

The latter the corpora striata give rise to certain 
voluntary and involuntary automatic acts, which are 
usually under the influence of the cells of the cortex, 
but, at times, act independently of them. The pulvinar 
of the optic thalamus, the corpora geniculata externa, 
and the colliculi anteriores are the sub-cortical centres 
for sight : and, by means of the optic radiation, are 
united with the cortical centres located in the occipital 
lobes. 

The Colliculi posteriores or posterior pair of corpora 
quadrigemina, and the corpora geniculata interna are 
the sub-cortical centres of hearing. Through the 
auditory radiations they are connected with the cortical 
auditory centres in the temporal lobe. 

The Red Nuclei are the primary terminations of 



2i8 THE CENTRAL NERVOUS SYSTEM 

the brachia conjunctiva superior peduncles of the 
cerebellum. New relays of fibres, starting in these 
nuclei, unite them with the optic thalamus, with the 
cerebral cortex, with the nuclei of origin of motor 
cranial nerves, and with the grey matter of the anterior 
horns of the spinal cord. 

B. The CEREBELLUM. The grey matter of the 
cerebellum, like that of the cerebrum, consists of 
cortical and sub-cortical ganglia. By the three cere- 
bellar peduncles these ganglia are brought into relation 
with the cerebrum, with the pons, with the medulla, 
and with the spinal cord. The chief sub-cortical ganglia 
of the cerebellum are the corpora dentata in the 
lateral lobes of the cerebellum, and the roof nuclei in 
the vermis cerebelli. Of the functions of the cere- 
bellum, we, as yet, know little. It is associated with 
the maintenance of equilibrium and with the co-ordina- 
tion of muscular movements. Moreover, it is quite 
possible that specific portions of its cortex are associated 
with definite groups of muscles. 

C. CRURA CEREBRI, PONS, and MEDULLA. The 
rest of the grey matter of the central nervous system, 
extending from the aquaeductus cerebri (Sylvius) to the 
filum terminale is entirely sub-cortical. It is arranged 
in a dorsal part, behind the central canal sensory in 
function ; and a ventral part, in front of the central 
canal motor in function. In the cerebral peduncles, 
pons, and medulla this grey matter forms the sub- 
cortical nuclei of origin or of termination of the several 
cranial nerves found in these regions. Thus, from the 
grey matter of the aquaeductus cerebri (Sylvius) arise 
the 3rd, the 4th, and the upper root of the 5th cranial 
nerves ; from the pons spring the 5th, the 6th, the /th, 



BRAIN, GENERAL SUMMARY 219 

and part of the 8th cranial nerves; and from the 
medulla arise the 8th, gth, loth, nth and I2th cranial 
nerves. Finally, at the lower part of the medulla, we 
find two nuclei, the nucleus gracilis and the nucleus 
cuneatus, which are the primary terminations of the 
long sensory strands Goll and Burdach of the 
posterior columns of the spinal cord. 

D. In the SPINAL CORD the grey matter is arranged 
in a series of columns vesicular columns which are 
the deep or sub-cortical origins or terminations of the 
motor and sensory spinal nerves. 

White Matter. The white substance of the central 
nervous system consists principally of the axis-cylinder 
processes of the nerve-cells which constitute the grey 
matter. It can be arranged in two distinct strands of 
fibres short strands and long strands. 

i. The SHORT STRANDS comprise the various Com- 
missures, such as the corpus callosum, the anterior and 
posterior commissures : Association fibres, and Projec- 
tion fibres, such as ihefornix, the anterior and posterior 
longitudinal bundles, and the cerebellar peduncles. In 
the spinal cord the association fibres join segments 
at one level with those at another, and occupy the 
regions of the cord known as the fasciculi proprii or 
mixed zones. Many of them are concerned with reflex 
acts. 

(1) The fornix, the corpus callosum, and other minor 
commissures have already been sufficiently described on 
pages 172 and 175. 

(2) The anterior or ventral longitudinal bundle 
tecto-spinal tract starts at the nerve-cells of the 
colliculi anteriores. After decussating with its fellow in 
themiddle line, beneath the floor of theaqu?eductus cerebri, 



220 THE CENTRAL NERVOUS SYSTEM 

the tecto-spinal tract descends through the cerebral 
peduncles, through the pons, and through the medulla 
to the anterior funiculus of the spinal cord, where it lies 
close to the anterior mesial fissure (fig. 17, page 22). 
On its way it gives fibres to the nuclei of motor cranial 
nerves, and to the cells of the anterior horn of the spinal 
cord of both sides. It is concerned with ocular and 
pupillar reflexes. 

(3) The posterior longitudinal bundle, which at first, 
lies within the fasciculus proprius of the anterior column 
of the spinal cord, is gradually pushed backwards, by 
both the motor and sensory decussations, from the 
ventral aspect of the spinal cord to the dorsal aspect 
of the medulla, pons, and cerebral peduncles. It 
contains both ascending and descending fibres. Both 
its origin and connections are much discussed. It 
probably carries fibres which, by means of terminals 
and collaterals, unite the nuclei of the several motor 
cranial nerves with each other, co-ordinating the nerves 
of the one side with those of the opposite side. It also 
receives fibres from the auditory tract, and from the 
nucleus of Deiters and other contiguous nuclei. The 
fibres from Deiters' nuclei, by their ascending and 
descending branches, are connected, on the one hand, with 
the nuclei of the 3rd and 6th cranial nerves, and, on 
the other, with the cells of the anterior horn of the 
spinal cord. They, therefore, form a secondary vestibular 
tract, between the nuclei of the vestibular division of 
the auditory nerve and these cranial and spinal nerves 
respectively. The posterior longitudinal bundle, more- 
over, unites peripheral sensory nerves with the cells of 
origin of the motor cranial nerves, e.g. the centres for 
the movements of the eyeballs with the visual centres. 



BRAIN, GENERAL SUMMARY 221 

(4) The peduncles of the cerebelluw are three in 
number the superior, the middle, and the inferior. 
They unite the cerebellum to the cerebrum, to the pons, 
to the medulla and to the spinal cord. 

(a) The brachia conjunctiva, or superior peduncles 
of the cerebellum, carry impulses from the corpus 
dentatum of the cerebellum to the red nucleus of the 
opposite side. New sets of fibres start in these nuclei : 
one set ascends to the optic thalamus and through it to 
the cerebral cortex ; another set rubro-spinal tract 
travels from the red nucleus of the one side, through 
that of the opposite side, to the lateral column of the 
spinal cord, where it lies, in front of the crossed 
pyramidal tract. A third set goes to the nuclei of 
motor cranial nerves. 

Since the cells of Purkinje" of the cortex cerebelli are, 
by means of their axones, joined with the cells of the 
corpus dentatum of the cerebellum of the same side, 
which, in turn, are connected, through the superior 
peduncles of the cerebellum, with the red nucleus of 
the opposite side, we can easily understand how it is 
that the cerebellar cortex of the one side is, through 
the red nucleus, and through the rubro-spinal tract, 
brought into relation with the cerebral cortex of the 
opposite side, and with the spinal cord of the same 
side. 

(b) The brachia pontis, or middle peduncles of the 
cerebellum, carry fibres from the nucleus pontis to and 
from the cerebelli of both sides. This nucleus is also 
connected through the cortico-pontine fibres with the 
cortex of the frontal, temporal, and occipital lobes of 
the cerebrum. 

(c) The restijorm body, or inferior peduncle of the 



222 THE CENTRAL NERVOUS SYSTEM 

cerebellum, has a very complex constitution ; see page 
ill. It is sufficient to state that it receives fibres from 
the lateral column of the spinal cord of its own side, 
from the posterior columns of the medulla of both sides, 
and from the inferior olive of the opposite side. 

Thus we see that each half of the cerebellum is 
brought into relation with the opposite cerebral cortex, 
with both sides of the medulla, and with the same side 
of the spinal cord, thus co-ordinating the muscles of the 
limbs of its own side. 

2. The LONG STRANDS projection fibres connect 
the motor-sensorial areas with lower centres. They 
are arranged in two groups : the one motor, the other 
sensory. 

The MOTOR STRANDS are two-fold, the cortical 
which are associated with voluntary movements, and 
the sub-cortical which are associated with involuntary 
movements. The former are again sub-divided into 
cortico-cranial and cortico-spinal tracts. Both these 
cortical motor tracts consist of two sets of neurones : 
the one central crossed; the other perepheral 
uncrossed. 

CORTICAL MOTOR STRANDS. 

(i) The CORTICO-CRANIAL motor tracts connect the 
cells of the cerebral cortex their first trophic realm 
with the sub-cortical centres second trophic realm 
of the motor cranial nerves. They start as the axis- 
cylinder process of the cells of Betz of the lower fourth 
of the ascending frontal convolution, and passing 
through the centrum ovale, occupy the middle segment 
of the corona radiata. They constitute the geniculate 
fasciculus, which traverses, firstly, the genu of the 
internal capsule, then the innermost segment of the 



PLATE XXXIII. 



KK;. 93. 
Motor and Sensory Tracts. 



Nucleus 
pontis. 
Cortico - 
ontine tract 




FIG. 94. 
Descending degeneration. 



1. Cortical areas. 



Inter. 



capsule. 2. Internal capsule 



Pyramidal 
tract 



Dorso-spino-ctrebeUai . 



Post, 




Brachia ponti*. 
Pans. 

Cerebellum 
Medulla.. 

Decussation of 
pyramids. 

j t Uncrossed and 

_. mossed pyramidal 

tracts. 

ft) Direct pyramidal tract 
i^nsary fibres. 
Spinal cord. 




-FascGoll. 

fate Bvrdach. 
Crossed pyr t. 
Direct pyr t. 



6. Spinal cord. 

i Crossed pyr t. 
. Direct pyr t. 

Motor Areas 
in each case coloured red 




Ant. nerve root 



U* Lg.n 4 Churning. Edmb jr Jh 



BRAIN, GENERAL SUMMARY 223 

crusta of the crura cerebri, and thus reaches the pons 
and the medulla. In each of these regions of the 
brain, the fibres, intended for the various motor cranial 
nerves, leave the main strand, and crossing the middle 
line, decussate with similar sets of fibres of the opposite 
side, to end at the several sub-cortical ganglia of the 
motor cranial nerves which are found in these regions. 

(2) The CORTICO-SPINAL motor tracts are divided in- 
to two groups, a principal motor strand, and a secondary 
motor strand (fig. 93, page 222 ; fig. 95, page 228). 

(a) The Principal Motor Strands arise, like the one 
previously described, from the cells of Betz the first 
trophic realm in the upper three-fourths of the 
ascending frontal convolution and in the contiguous 
paracentral lobule. At their origin they form a fan- 
shaped group of nerve-fibres, which spread out trans- 
versely to the long axis of the cerebral hemispheres. 
They occupy the middle segment of the corona radiata, 
and, descending through the anterior two-thirds of the 
posterior limb of the internal capsule, behind the 
geniculate fasciculus, they enter the central division of 
the crusta of the crura cerebri, through which they 
pass to the ventral aspect of the pons and medulla. 
At the lower limit of the medulla, this motor strand 
splits up into three groups of fibres ; one group, forming 
about 90 per cent of the motor fibres, decussates at the 
bottom of the anterior median fissure of the medulla 
decussation of the pyramids with those of the opposite 
side, and then descends, as the crossed pyramidal tract, 
in the opposite lateral column of the spinal cord to 
reach the perepheral motor neurones situated in the 
anterior horns the second trophic realm. A second 
group, about 10 per cent, pass down the anterior column 



224 THE CENTRAL NERVOUS SYSTEM 

of the cord of their own side as the direct pytaviidal 
tract, to cross over individually at lower levels, through 
the anterior commissure, to the grey matter of the 
opposite side of the spinal cord. Finally, a few fibres, 
forming a third group, the uncrossed lateral pyramidal 
tract, come from the cerebrum of its own side, and 
neither cross, in the medulla nor in the spinal cord, but 
remain on its own side through their entire course, 
hence we find that, in cases of hemeplegia one-sided 
paralysis the sound side shows a certain degree of 
weakness, the injured side a certain amount of 
movement (fig. 93, page 222). 

In the cortex cerebri the motor centres are arranged 
from below upwards in the following order (i) the 
face and neck ; (2) the fingers, wrist, elbow, shoulder ; 
(3) the trunk ; (4) the hip, knee, ankle, toes : in the 
internal capsule the motor fibres are grouped, from 
before backwards as follows: (i) in the genu we have 
fibres for the eyes, head, mouth, and tongue ; (2) in the 
anterior two-thirds of the posterior limb we find first, 
the fibres for the shoulder, then those for the elbow, 
wrist, fingers, thumb, trunk, hip, knee, ankle, and toes. 
Thus we see that the grouping of the fibres for the 
upper limb is different in the capsule from what it is 
in the cortex, for whereas in the cortex the fibres for 
the fingers are next those for the face, in the capsules 
those for the shoulders are next those for the face. 

We have just seen that the axis-cylinder processes 
of the motor strands, which constitute the cranial nerves, 
as they descend through the crura cerebri, pons, and 
medulla, on their way from the cerebral cortex, cross 
over to the opposite side, and, by means of their 
collaterals and terminals, come into relation with the 



BRAIN, GENERAL SUMMARY 225 

peripheral neurones of the several motor cranial 
nerves, so also, at lower levels, do the fibres intended 
for the spinal nerves, decussate in the pyramids or 
in the spinal cord (fig. 93, page 222). The central 
neurones therefore carry the impulses from the brain 
to the cranial and spinal peripheral motor neurones 
of the opposite side, which in turn transmit them 
to the muscles. Thus, for example, the right side 
of the face or arm is worked from the right facial 
or spinal nucleus the sub-cortical origin ; but from 
the left cerebral cortex the cortical origin. Hence it 
follows, that the strands from the peripheral motor 
neurones are uncrossed, whereas these from the central 
neurones are crossed. 

The following cranial nerves are exceptions to 
this rule: the 3rd and the I2th nerves are partially 
crossed ; the 4th nerves are totally crossed, decussat- 
ing in the superior medullary velum, after leaving the 
brain. 

() 77ie Secondary Motor Strands. The cortico- 
cerebellar spinal have their central neurones in the 
same areas as the cells of the principal motor tracts, 
and their axis-cylinders descend, mingled with those of 
the chief motor tract, through the internal capsule 
arid crura cerebri to the pons, where they leave that 
strand, and end in branches amidst the nerve-cells of 
the nucleus pontis. The axis-cylinders of the nerve- 
cells of this nucleus nucleus pontis then cross over 
to the opposite half of the cerebellum, to terminate at 
the neurones of the cerebellar cortex, which in turn 
transmit the impulses, probably through the cells of 
Deiters' nucleus, to the spinal cord, thence to the grey 
matter of the anterior cornu, and thus to the muscles. 

Q 



226 THE CENTRAL NERVOUS SYSTEM 

This, then, is also a crossed tract, the crossing taking 
place in the upper set of neurones (fig. 95, page 228). 

SUBCORTICAL MOTOR STRANDS. 

The SUBCORTICAL MOTOR STRANDS take their origin 
in the corpus striatum, which is one of the principal 
basal ganglia. They form a strio-spinal motor system, 
which can originate elementary and primitive move- 
ments, automatic in character, independent of the 
cerebral cortex, but normally under its control. On 
page 1 66 we have seen that the corpora striata each 
consists of three nuclei, the nucleus caudatus, the nucleus 
lenticularis, and the claustrum. The lenticular nucleus 
is again subdivided into the globus pallidus and the 
putamen. These differ somewhat in structure, for, 
whereas the globus pallidus has many large ganglionic 
cells, motor in function and giving origin to the pallidal 
or strio-spinal motor system : the nucleus caudatus and 
the putamen have few large cells but many small ones, 
which by their axis-cylinder processes are connected 
with the cells of the globus pallidus They form an 
inhibitory and co-ordinating system, for whereas destruc- 
tion of the cells of the globus pallidus results in muscular 
rigidity, in tremors and in disturbance of automatic 
movements, injury to the inhibitory system give rise 
to movements that are choreic or epileptical in 
character. (Purves Stewart.) 

The strio-spinal or pallidal system, uniting the corpus 
striatum with the motor cells of the anterior horn, is 
also connected with lower subcortical centres situated 
in the crura, pons, and medulla, which, in turn, are 
associated with the nerve-cells of the anterior horn of 
the spinal cord. 



BRAIN, GENERAL SUMMARY 227 

The following are the chief subcortical motor 
strands : 

(1) The strio-spinal, from the cells of the globus 

pallidus. 

(2) The rubro-spinal, from the cells of the red 

nucleus in the crura cerebri (see page 188). 

(3) The tecto-spinal, from the reflex centres for 

the eyes and the ears, in the corpora quad- 
rigemina. 

(4) The vestibulo-spinal, from the accessory nucleus 

of Deiters in the pons to the cells of the 
anterior horns of the spinal cord. 

(5) The ponto-spinal, from cells in the formatio 

reticularis through the anterior column of 
the same side and the lateral column of the 
opposite side, to the cells of the anterior 
horns of the spinal cord. 

Thus, we see that, whereas the cells of the cerebral 
motor cortex, with their cortico-cranial and cortico- 
spinal tracts, control voluntary movements ; on the 
other hand the cells of the globus pallidus with the 
pallidal or sub-cortico-spinal system, control certain 
automatic movements. 

(2) THE SENSORY STRANDS conduct impulses from 
the periphery to the brain. They consist of two 
segments a lower segment the median band of Reil 
which extends from the lower sub-cortical ganglia 
of Spinal and cranial nerves to the optic thalamus ; and 
an upper segment, which extends from the optic 
thalamus to sensory areas of the cerebral cortex. They 
have a peripheral and a central set of neurones. 

The peripheral neurones are uncrossed and single. 
Their cells are situated outside the cerebro-spinal axis, 



228 THE CENTRAL NERVOUS SYSTEM 

in the spinal ganglia, in the case of the spinal nerves, 
and in the ganglia of the sensory nerves, in the case 
of the cranial nerves. The cells of these ganglia have 
a peripheral process the protoplasmic process which 
places the surface of the body and the various sense 
organs in communication with the cells of these 
ganglia; and a central process the axis-cylinder 
process connecting the cells of the ganglion with the 
central axis. They are, as we have said, uncrossed. 
The central neurones connect these peripheral neurones 
with the higher nerve-centres. These are situated within 
the central nerve-axis, and consist of at least two sets 
of superimposed neurones. They are crossed, the 
crossing taking place either in the spinal cord, the 
inferior sensory decussation, or in the medulla the 
superior sensory decussation, or in case of the cranial 
nerves, at higher levels. 

In the spinal cord the chief sensory strands are 
the lateral cerebellar tract, the fasciculus of Gowers, the 
fasciculus of Goll, and the fasciculus of Burdach. 

(c) The fasciculi of Goll and of Burdach were 
traced into the medulla as the fasciculus gracilis and 
the fasciculus cuneatus. They end in the nuclei of 
these fasciculi. Thence second relays of fibies carry 
the impulses one of two ways, either (i) through the 
inferior cerebellar peduncle to the cerebellum of the 
same side or opposite side, or (2) through the medulla 
sensory decussation, or decussation of the fillet- 
through the pons, through the crura cerebri, and through 
the posterior part of the internal capsule to the opposite 
cerebral hemispheres. A few of the fibres go direct to 
the cerebral cortex ; but most of them first pass through 
the optic thalamus (fig. 93, page 222). 



PLATE XXXIV. 



Pyram 
tracts. 



Cortico-pontine fibres. 



Nuclei of 
9th, IQth, \\th 
nerves. 




Post. long, bundle. 
Cerebellum. 



Restiform 
body. 



Uncrossed 
pyramidal tracts. 



Motor Tracts, 



V.' L(M * Camming. Edrabur, 



PLATE XXXV. 



Optic radiation 



2nd 



Corpus 
dentatum. 



7 asc. ffracilisGoli. 
. - Fasc. cuneatus Biirdach 



i Posterior roots 
and ganglia. 




Bulbo- 

'tkalamic t. 



Gangiia of post. root. 



Sensory Tracts. 



BRAIN, GENERAL SUMMARY 229 

(b) The ascending antero -lateral tract of Gowers, 
lying, as you know, on the surface of the lateral aspect 
of the cord in front of the direct cerebellar tract, is a 
composite strand. One part of it, the ventro-spino- 
cerebellar, can be traced upwards to the pons, to the 
level of the 5th cranial nerve, where it turns downwards 
and backwards to enter the brachium conjunctivum. 
It ends in the lingual lobe of the superior vermis 
cerebelli of its own side. Another set of fibres 
spino-tectal reaches the pons and mid-brain. A third 
set spino-thalamic ascends, through the posterior 
limb of the internal capsule to the optic thalamus and 
to the cerebral cortex, carrying sensations of touch, of 
temperature, and of pain from the posterior spinal 
nerve-roots. It is a crossed tract through the cells 
of the posterior column. 

(a) The lateral cerebellar or dorso-spino-cerebellar tract 
ascends along the lateral margin of the spinal cord and 
medulla to the inferior peduncle of the cerebellum, 
thence to the upper part of the superior vermis. Most 
of its fibres end in the same side. This tract, which is 
associated with the co-ordination of muscular move- 
ments, is connected by means of the cells of Clarke's 
column with the posterior spinal nerve-roots. 

In the brain the chief sensory strands are the fillet 
or lemniscus, and the groups of the nerve-fibres which con- 
stitute the sensory cranial nerves. 

The fillet is the strand of nerve-fibres which conveys 
sensory impulses to the cerebral cortex from the 
posterior spinal nerve-roots, from the auditory nuclei 
of the medulla and pons, and from the sensory nuclei 
of other cranial nerves. It is divided into two parts : 
the mesial or main fillet, and the lateral fillet. 



230 THE CENTRAL NERVOUS SYSTEM 

(a) The main or mesial fillet is the continuation 
upwards of the posterior columns of the spinal cord 
through the nuclei of the fasciculus gracilis and the 
fasciculus cuneatus of the medulla. The former receives 
the fibres from the lower limbs, the latter from the 
upper limb. In the mesial line of the medulla, in the 
inter-olivary region, the fibres of the fillet decussate 
\\ith those of the opposite side, constituting the 
superior sensory decussation or decussation of the 
fillet, as distinct from the inferior sensory decussation 
in the anterior commissure of the spinal cord. After 
decussating, the sensory fibres form a distinct strand, 
the main or mesial fillet, which passes through the 
dorsal part of the medulla, pons, and cerebral peduncles, 
and receiving fibres from the sensory nuclei of cranial 
nerves, and being joined in the pons by the spino- 
thalamic tract, ascends to the optic thalamus and to the 
region below it. Thence a new relay of fibres carries 
the impulses through the posterior limb of the internal 
capsule to the cortical centres for sensation, chiefly 
situated in the post-central gyrus. The fillet is thus 
a crossed sensory tract, carrying tactile sensations and 
sensation from muscles, from bones, and from joints 
to the cortex cerebri. In the mid-brain the mesial 
fillet gives off a small bundle of fibres the superior 
fillet to the anterior pair of corpora quadrigemina 
colliculi anteriores. 

Thus we see that sensations of touch, of temperature, 
and of pain cross in the spinal cord inferior sensory 
decussation, whereas sensations from muscles, from 
joints, and from bones cross in the medulla superior 
sensory decussation. 

(b) The lateral fillet is the upward continuation of 



BRAIN, GENERAL SUMMARY 231 

the central auditory tract. As you already know, the 
accessory and lateral auditory nuclei are the primary 
terminations of the cochlear division of the 8th cranial 
nerve. From these nuclei the auditory fibres travel 
either by way of the corpus trapezoid of the pons, 
or through the striae medullares of the 4th ventricle, 
to the nucleus of the corpus trapezoideum and to the 
superior olive of the same, but mostly of the opposite 
side. Thence, by new relays of fibres they reach the 
nucleus of the lateral fillet, the corpora geniculata 
interna and the colliculi posteriores, a few only ending 
in the colliculi anterieses. From these nuclei the 
auditory tract travels to the cortical centres for hearing, 
situated in the superior temporal gyrus and upper 
surface of the temporal lobe. Thus we see that each 
ear is connected with the cortical centres of both sides, 
but mainly with that of the opposite side. The lateral 
fillet is also connected with the lateral column of the 
spinal cord. 

For the course followed by the several nerves of 
special sense and other sensory cranial nerves, see 
Origins of Cranial Nerves, page 197. 



23 2 THE CENTRAL NERVOUS SYSTEM 



SECTION III. 



OUTLINE OF DEVELOPMENT. 

IN this section we shall give an outline of the develop- 
ment of the brain and spinal cord. 

One of the earliest steps in the development of the 
human embyro is, as you know, the formation of the 
blastoderm or germinal membrane. This membrane is 
composed of three distinct superimposed layers of 
cells, the ectoderm, the mesoderm and the entoderm. Of 
these, the ECTODERM is the one from which the central 
nervous system is developed. 

NEURAL GROOVE. On the dorsal aspect of the 
embryo, at a very early date, we find, in front of the 
primitive streak, two longitudinal ridges, separated from 
each other by an intervening furrow the primitive 
neural groove. Gradually increasing in size, these two 
ridges grow backwards and ultimately meet in the 
middle line on the dorsal aspect of the embryo. 
Blending together in the middle line, they form a 
closed, cylindrical, longitudinal tube the primitive 
neural tube with walls composed of ectodermic cells 
(fig. 97, page 238). From this primitive tube the brain 
and spinal cord are formed ; the walls giving rise to 
the solid parts, viz. to the neuroglia and to the nerve- 
cells and their processes ; the cavity remaining either 
as the central canal of the spinal cord, or as the 
various ventricles of the brain. Along the line of 
junction of the two lateral walls, on the dorsal aspect 



DEVELOPMENT, SPINAL CORD 233 

of the neural tube, is a ridge of ectodermic cells, which 
unites the embedded with the surface ectoderm. This 
ridge forms the neural crest. From its cells are 
developed the ganglia of both the sympathetic, and 
the cerebro-spinal nervous systems (figs, a, b, c, page 238). 

I. THE SPINAL CORD. 
(Figs. 97, etc., Plate XXXVI. Page 238.) 

The Spinal Cord is developed from the hinder part 
of the primitive neural tube. The lateral walls of this 
portion of the tube increase in thickness, so much so 
that the cavity of the tube is reduced to a mere longi- 
tudinal slit. Its roof and floor, however, remain thin, 
and form the mid-dorsal and mid-ventral lamina. 
At first the wall of the neural tube consists of a single 
layer of ectodermic columnar cells, these undergo rapid 
divisions resulting not only in the thickening of the 
lateral walls, but also in the formation in these walls of a 
SYNCYTIUM, a close network of dense protoplasm, beset 
with numberless nuclei, but with the outlines of the 
individual cells very indistinct. Becoming looser in 
texture, and forming an open spongy reticulum, tra- 
versed by strands of cells which radiate sideways at 
right angles to the lumen of the tube, this syncytium, 
which is bounded on each side by limiting membranes, 
can be subdivided into three more or less distinct layers ; 
(i) an inner one, near the central cavity, crowded with 
nuclei; (2) an outer one, near the surface, forming a 
network of fibres without nuclei ; and (3) a middle or 
mantle layer also dotted with many nuclei. The cells 
of the inner layer become the ependyma or lining 
cells of the central canal. The outer or marginal layer 



234 THE CENTRAL NERVOUS SYSTEM 

forms the supporting framework of the future white 
columns of the spinal cord. The middle or mantle layer 
is the precursor of the cells of the grey matter of the 
spinal cord. It consists of two groups of cells, the 
germinal cells and the spongioblasts. 

The germinal cells occupy the lateral walls of the 
neural tube, there being no such cells in the mid-dorsal 
and mid-ventral laminae. They are grouped near the 
lumen of the tube between the deep ends of the 
ependyma cells. They are globular in outline, and 
though the bodies of the cells consist of only a small 
amount of clear protoplasm, the nuclei of the cells are 
large and well marked, and stain deeply with reagents. 
Increasing rapidly in number they give birth to two 
sets of cells the neuroblasts or young nerve-cells, and 
the spongioblasts or young neuroglia cells. 

The spongioblasts are so arranged that the inner 
ends of the cells unite to form an inner limiting 
membrane. The outer ends, on the other hand, are pro- 
longed outwards to form the myelospongium the fibrous 
net-work of the marginal zone. On the surface their 
terminal processes blend together to form the outer 
limiting membrane. 

The neuroblasts or young nerve - cells at first 
occupy the deep part of the lateral walls of 
the neural tube. Soon, however, they migrate, along 
with the spongioblasts, to the interval between the 
myelospongium and the ependymal cells. In this 
position they form a thick definite stratum the 
mantle layer, composed of cells with large distinct nuclei 
At first rounded or oval in shape, they soon become pear- 
shaped ; the narrow end or stalk of the pear elongating 
and growing out as the axone or axis-cylinder process 



DEVELOPMENT, SPINAL CORD 235 

of the nerve-cell. The body of the pear, on the other 
hand, becomes beset with numberless spinous processes, 
which finally break up into a reticulum of fine fibres. 
These fibres branch in all directions and constitute the 
dendrites of the protoplasmic processes of the nerve- 
cells. 

BASAL and ALAR LAMINAE (fig. 102, page 238). 
The mid-dorsal and mid-ventral laminae, as we have 
seen, undergo little change ; the inner aspects of the 
thickened lateral walls of the neural tube are, how- 
ever, each furrowed by a longitudinal, wide, shallow 
groove the limiting sulcus which is not confined to 
that portion of the tube which forms the spinal cord, 
but extend also to that part which will form the brain. 
These sulci subdivide each lateral half of the mesial wall 
of the neural tube into two longitudinal strips of nerve- 
substance, the one dorsal, the other ventral. The dorsal 
segment is known as the alar lamina, the ventral 
segment as the basal lamina. Into the former grow 
the axones from the ganglia of the posterior nerve- 
roots : from the latter spring the fasciculi which form 
the anterior nerve-roots. 

Thus we see that the walls of the original neural 
tube are so modified that they give rise to laminae, the 
subdivisions of which are given in the following table : 

f , /mid-dorsal, 
(mesial 

'-mid- ventral. 

Laminae -! 

, lateral dorsal or alar, 
(lateral ] . 

I lateral ventral or basal. 

Our next step is to study the formation (i) of the 
grey matter, (2) of the white matter, and (3) of the 
fissures of the spinal cord. 



236 THE CENTRAL NERVOUS SYSTEM 

I. THE GREY MATTER. The ventral division of the 
mantle layer forms a longitudinal mass, which is rich 
in neuroblasts, and which occupies the sight of the 
future anterior cornua of the spinal cord. The 
neuroblasts, which form it, arrange themselves in 
definite groups, corresponding with the groups in the 
future anterior horns. Many of the cells send out their 
axis-cylinder process towards the surface of the neural 
tube, to the place of origin of the future anterior nerve- 
roots. They constitute the fasciculi of these nerve-roots. 
The posterior horn is a subsequent backward outgrowth 
into the thin dorsal part of the mantle layer. Into it 
can be traced the central process of the ganglia of the 
posterior nerve-roots. Its formation is coincident with 
the development of the posterior white columns of the 
spinal cord. 

II. THE WHITE MATTER. On the surface of the 
cord, in the region in which its future white columns 
are developed, we find no nuclei, this part of the 
embryonic cord being composed of the myelospongium 
or reticular part of the spongioblasts. Into this 
reticulum the young nerve-cells neuroblasts send 
their axones. Of these, some grow outwards towards 
the points of exit of the future anterior nerve-roots ; 
others, becoming longitudinal ascend and descend in 
the reticulum, and give rise to the anterior and lateral 
columns or funiculi of the spinal cord. The posterior 
columns have a different origin. They arise by the 
ingrowth of the axones of the nerve-cells of the ganglia 
on the posterior nerve-roots. These axones penetrate 
the cord from without, and, dividing into ascending and 
descending branches, constitute both the posterior 
roots of the spinal nerves and the chief part of the 



DEVELOPMENT, BRAIN 237 

posterior columns of the cord. Thus we see that the 
anterior and lateral columns are the first to appear, 
then the posterior. 

As we have already seen in the account of the 
spinal cord, these white strands acquire their medullary 
sheaths at different dates, thus enabling us to map 
out the course they take through the spinal marrow. 

III. FISSURES. At first there are no indications 
of the anterior and posterior median fissures of the cord. 
The former, the anterior median fissure, is the cleft 
left between the enlarging lateral halves of the cord. 
The anterior commissure is developed at the bottom 
of this fissure, thus separating it from the central canal 
of the cord. The posterior median fissure is not a real 
fissure, but consists of a septum which is formed in part 
by the fusion of the mesial walls of the dorsal portion 
of the neural tube, and in part by the elongation of the 
processes of the ependyma cells as the dorsal white 
columns of the cord grow backwards. 

At first the spinal cord fills the entire length of the 
spinal canal, so that there is no cauda equina ; but, by 
the rapid growth of the canal as compared with the 
contained spinal marrow, the cord, at about the ninth 
month, reaches only as low as the 3rd lumbar vertebra. 
In the adult it usually reaches the ist lumbar vertebra. 

The membranes of the spinal cord are developed 
from the mesodermic tissue which grows round the 
original neural tube. 

We shall next turn our attention to the study of 
the development of the Brain, and its several sub- 
divisions. 



238 THE CENTRAL NERVOUS SYSTEM 

II. THE BRAIN. 
(Plate XXXVI. Page 238). 

The Brain is formed from the fore part of the 
primitive neural tube. At the period of development, 
when the posterior part of this tube is as yet open, 
the anterior portion dilates considerably, but at first 
remains single. Its walls become thickened and the 
cavity of the tube is subdivided by two constrictions 
into the three segments known as the anterior, the 
middle, and the posterior primary cerebral vesicles, 
or the Prosencephalon the fore-brain : the Mesence- 
phalon the mid-brain : the Rhombencephalon the 
lozenge-shaped or hind-brain. The fore part of the Rhom- 
bencephalon, that next the Mesencephalon, is constricted, 
and is therefore called the Isthmus Rhombencephali. 
The anterior and posterior primary vesicles soon divide 
into two, one behind the other, whereas the middle 
primary vesicle remains single. Thus we get five 
secondary vesicles (tig. 97, page 258) formed from the 
three primary vesicles, These five secondary vesicles 
are named the Telencephalon or end-brain : the Dience- 
phalon or inter-brain : the Mesencephalon or mid-brain : 
the Metencephalon or after-brain : the Myelencephalon 
or marrow brain. 

The following table will give you, enumerated from 
before backwards, the names of the primary and 
secondary vesicles and will furnish you with a list of 
the parts developed from each vesicle : 



PLATE XXXVI. 



FIG. 97. 



fiem ispheri 
vesicle 



Prosencepha Ifrrr 
fore brain. 



Telen- 
ephalon. 



I J Dien- 

\ \f- I cephalon. 



FIG. 98. 

Corpora 
rebi-a I \^a uadrigem inn . 



Cerebellum. 
'Medulla. 



FIG. 99. 






Mesencephalon. ) 







Mesen- 



mid brain. 



Rhomben- 
cephalon. 



i J- Meten- Corpus 

\ / cephalon. FIG. 100. cattosum 

/ \ ~-~^~~\~, T'-/.^j.Jt ^"^ y?E 



FIG. 101. 



Telenceph 
Mesenceph. 

Dienceph. 
Rhombenceph. 



Optic 
thalamus. 



Myelen- 



cephalon 
hind brain. \ f 



S. cord. 




Ectoderm -. 
Afesodrrm. 

Ectoderm 



peduncles. ^-Medulla. 
Ntural Canal. 




Corpus 
striatum 



Olfactory 
lobe 



H- L. t ui A CuMmui(. Edinburgh 



DEVELOPMENT, BRAIN 



2 39 



TABLE OF THE CEREBRAL VESICLES AND THE PARTS 
DEVELOPED FROM EACH. 



PRIMARY 
VESICLES. 



SECONDARY 
VESICLES. 



i. Prosen- 

cephalon 



i. Telencephalon 



2. Diencephalon 



PARTS DEVELOPED FROM THE 
VARIOUS VESICLES. 

Cerebral Hemispheres. 
Corpora Striata. Cor- 
pus Callosum. Fornix. 
Lateral Ventricles. Ol- 
factory Lobe. Fore 
part of 3rd Ventricle. 
Fore part of the Tuber 
Cinereum. Infundi- 
bulum. Posterior Lobe 
of Pituitary Body. 

Optic Thalami. Corpora 
Geniculata. Pineal 
Body. Posterior part 
of the Tuber Cinereum. 
Posterior part of 3rd 
Ventricle. Corpora 
Mammillaria. Optic 

Nerve and Tracts. 



[ Corpora Quadrigemina. 

-> Mesen- Pedunculi Cerebri. 

J3. Mesencephalon J A 
cephalon \ j Aquaeductus Cerebri. 

(Sylvius). 



4. Metencephalon 



3. Rhomben- 
cephalon 



rThe Cerebellum. Pons 
J. Varolii. Anterior part 
\ of the 4th Ventricle. 



(Medulla Oblongata. Pos- 
terior part of 4th Ven- 
tricle. 



6. 



Isthmus Rhoinb- 
encephali 



The Superior Cerebellar 
Peduncles. Valve of 
Vieussens. 



240 THE CENTRAL NERVOUS SYSTEM 

Thus we get five rings, with ectodermic walls, 
composed of histological elements similar to those 
which give origin to the spinal cord. By subsequent 
changes in these rings the brain and its subdivisions 
are built up. 

1. The Rhombencephaion POSTERIOR CEREBRAL 
VESICLE gives origin to the medulla oblongata, to 
the pons Varolii, and to the cerebellum. Bending for- 
wards at the upper or anterior end of the primitive spinal 
cord and forming the cervical flexure (fig. 103, page 
238), the posterior vesicle makes a second knee-shaped 
bend backwards on itself. At first single, this vesicle 
soon becomes divided by a constriction into two parts, 
a posterior division the Myelencepkalon, and an 
anterior division the Metencephalon, 

The hinder division of the vesicle the Myel- 
encephalon, forming the forward bend, becomes 
developed into the MEDULLA, and the lower part of 
the 4th VENTRICLE. 

The backward fold forming the fore-part of the 
original vesicle the Metencephalon becomes the 
CEREBELLUM and the upper part of the 4th VENTRICLE. 
The knee-shaped bend itself gives rise to the PONS 
VAROLII ; hence it is often called the pons curvature. 

The Isthmus rhombencephali the constructed part 
between the posterior and middle cerebral vesicles 
becomes the superior cerebellar peduncles and the 
valve of Vieussens (fig. 102, page 238). 

2. The Meseneephalon MIDDLE CEREBRAL VESICLE 
likewise bends forwards on the posterior vesicle, but, 
unlike the other primary vesicles, does not divide, but 
remains single. Its roof alar lamina becomes 
thickened, and in it are formed the CORPORA QUADRI- 



DEVELOPMENT, BRAIN 241 

GEMINA. Its floor and sides basal lamina give rise 
to the PEDUNCULI CEREBRI, while the original CENTRAL 
CANAL, much narrowed by the growth of these parts, 
remains as the AQU^DUCTUS CEREBRI (Sylvius) iter a 
tertio ad quartum ventriculum. 

3. The Prosencephalon ANTERIOR CEREBRAL 
VESICLE, like the posterior, becomes sub-divided into 
two portions a posterior the Diencephalon, and an 
anterior, the Telencephalon. The entire vesicle, at 
first single and straight, bends forwards on the middle 
vesicle, giving rise to the cephalic flexure, which now 
forms the most prominent part of the head (fig. 103, 
page 238). Before it divides into its segments, two 
hollow club-shaped diverticula the OPTIC VESICLES and 
OPTIC STALKS, grow out from its side walls. They 
ultimately become the retina and the optic nerves (fig. 
103, page 238). 

Diencephalon. From the altar division of the lateral 
walls of this segment the diencephalon are developed 
the two OPTIC THALAMI, separated from each other by 
a median cleft the 3RD VENTRICLE. Across this 
cavity is subsequently formed the massa intermedia, 
the middle or grey commissure. In the floor of the 
ventricle are formed the CORPORA MAMMILLARIA and 
the posterior part of the TUBER CINEREUM all of 
which structures have been seen in the interpeduncular 
space. At the back, the cavity communicates with the 
4th ventricle through a narrow channel the aqueduct 
of Sylvius, the continuation backwards of the original 
cavity ; in front, through the interventricular foramina, 
it communicates with the lateral ventricles. 

The roof of the vesicle rapidly becomes thinner, 
and is ultimately reduced to a mere lamina of epi- 

R 



242 THE CENTRAL NERVOUS SYSTEM 

thelium connected with the pia mater and with the 
choroid plexus in the roof of the 3rd ventricle. The 
posterior part of the roof, however, has a transverse 
thickening the POSTERIOR COMMISURE in front of 
which the roof grows at first upwards and forwards, 
then backwards as a hollow process the PINEAL BODY 
or epiphysis cerebri which lies in the groove between 
the anterior pair of corpora quadrigemina. 

Telencephalon. The fore part of the original 
anterior cerebral vesicle telencephalon bulges forward 
as a median thin walled vesicle which is at first single, 
but soon becomes divided by a longitudinal cleft into 
two lateral segments, united by a thin mesial part at 
the bottom of the cleft. The wall of the central segment, 
in other words, the bottom of the cleft, remains thin 
and stationary, and forms the lamina terminalis. The 
cavity of the mesial segment becomes the fore part of 
the 3RD VENTRICLE, and in its floor are formed the 
anterior part of the TUBER CINEREUM, the INFUNDI- 
BULUM, and the posterior lobe of the PITUITARY BODY. 
The lateral segments, on the other hand, grow rapidly 
and form the hemispherical vesicles, which become 

the CEREBRAL HEMISPHERES (fig. 103, page 238), 

the cavities within them remaining as the LATERAL 
VENTRICLES. These are connected with the 3rd 
ventricle, and, through it, with each other, by a 
constantly narrowing neck, the FORAMEN INTERVEN- 
TRICULARE (Monro) fig. 97, page 238). In the floor 
of each of these ventricles appears a grey mass the 
CORPUS STRIATUM, streaked with white matter, giving 
it the striated appearance from which it takes its 
name. Outside this grey mass we find the grey and 
white matter of the Island of Reil. On page 127, we 



DEVELOPMENT, BRAIN 243 

saw that these cerebral hemispheres could each be sub- 
divided into two parts, the pallium, and the rhinen- 
cephalon. This subdivision is recognisable at a very 
early date, the line of demarcation being a slight 
lateral furrow on the surface of the hemispheres. In 
the human brain the rhinencephalon is very rudi- 
mentary and the pallium enormously developed. 

The OLFACTORY LOBES are hollow outgrowths of 
the lower and lateral parts of the hemispherical 
vesicles. 

The roof and walls of the hemispherical vesicles 
are, at first, an evenly expanded mass of grey matter. 
This, however, soon becomes convoluted and fur- 
rowed, giving rise to the fissures, lobes, and gyri of 
the cerebral hemispheres. Of these fissures, some are 
infoldings of the entire wall, and cause corresponding 
elevations in the interior of the vesicle ; these are the 
primary fissures : the sulci or secondary fissures arc 
mere grooves, and do not give rise to corresponding 
elevations in the interior. Increasing rapidly in size 
the hemispheres grow backwards, and, finally, com- 
pletely everlap and hide the other subdivisions of the 
brain. 

The Fornix, the Corpus Callosum, and the anterior 
commissure appear to take their origin in connection 
with the lamina terminalis ; but their exact mode of 
development is still very doubtful. However, in front, 
and for some distance backwards, the mesial surfaces 
of the cerebral hemispheres come in contact, and at 
certain places partly grow together. From these 
united parts of the mesial aspect of the hemispherical 
vesicles are developed, the CORPUS CALLOSUM, the 
FORNIX, and the ANTERIOR COMMISSURE. The 



244 THE CENTRAL NERVOUS SYSTEM 

anterior commissure is the first to be formed, then the 
fore part of the fornix, and afterwards its posterior 
pillars. Finally, the corpus callosum appears, the 
anterior part being the first developed, the rest of it 
extending backwards with the growth of the hemi- 
spheres. 

Those portions of the mesial walls of the hemi- 
spherical vesicles, which lie between the corpus callosum 
and the fornix, form, as they unite, two plates or 
laminae which become the septum lucidum, the vertical 
partition separating the lateral ventricles. Between the 
two layers of which this septum is composed, is the 
cavity of the 5th VENTRICLE, or ventricle of the 
septum, which you will readily understand is never 
connected with the rest of the ventricles, and is not, 
like them, part of the primitive medullary cavity. 



Accessory auditory (Cochlear) 

Nucleus, 125, 209 
Olives, 98, 103 
Achromatic Matter, 38 
Acusticum, Trigonum and 

Tubercle, 121, 209 
Area acustica, 121 
Ala Cinerea (Cinereus, ash- 
coloured), 121, 125, 211 
Alae Lobuli Centralis, 106 
Alar Lamina, 235 
Albicantia (Mammillaria), Cor- 
pora, 150, 159, 176 
Amgbiuus Nucleus, 210, 211 
Amygdala? (Amygdala, an 
almond) of Cerebellum, 107 
of Cerebrum, 158 
Nucleus, 158, 166, 167, 168 
Amylacea, Corpora (Pineal), 161 
Apex Cornu Posterioris, 32 
Aqueduct (Aquaeductus Cerebri) 
(Sylvius), 123, 154, 160, 191, 
239, 241 

Arachnoid (apaxfiov, a spider or 
spider's web), Membrane of 
Spinal Cord, 9 
Brain, 55 

Structure of, n, 55 
Subrarachnoid space, 10, 56 
Arbor Vitae (from resemblance to 
the shrub so-called) of Cere- 
bellum, 105, 113 

Arcuate or Arciform Fibres, of 
Medulla, 72, 79, 80, 91, 93, 
in 

Nucleus, 87, 93 
Area of Broca (Olfactory), 132, 

141 
Acustica, i2i, 208 



Areas, Association, 143, 175, 217 
Motor and Sensorial, 142, 

216 

of Medulla, 73 et seq. 
of Spinal Cord (Vascular), 13 
Arteries Auditory Internal, 64 
Basal Branches, 62 
Basilar, 63 
Brain, 61 
Cortical, 62 
Carotid, Internal, 61 
Cerebellar, Anterior Inferior, 
64 

Superior, 64 

Cerebral, Anterior, 61, 143 
Middle (Sylvian), 61. 143 
Posterior, 61, 144 
Circulation, special char- 
acter of, 65 

Choroidal, Anterior, 63 
Circle of Willis, 64, 65, 148 
Communicating Anterior, 62 

Posterior, 63 
Cortical, 62 
Lenticular, 182 
Lenticulo-striate, 182 
Meningeal, 60 

Special characters of the Cere- 
bral Circulation, 65 
Spinal Anterior, 12 

Anterior Median, 12 
Central, 12 
Centrifugal, 12 
Commissural, 12 
Posterior, 12 
Centripetal, 13 
Peripheral, 13 

ular areas, 13 
Table of Cerebral, 67 
Vertebral, 63 



245 



246 



INDEX 



Association Areas, 143, 175, 217, 
Fibres, 116 171, 175, 178, 219 
Table of, 178 

Astrocytes, 34 

Ataxy, Locomotor, 26 

Auditory Nerve, 207 
Cochlear division, 209 
Vestibular division, 208 
Nuclei, 124, 125, 208, 209 
Radiation, 180, 210 
Table of, 213, 214 
Tracts, 208, 210, 213, 214 

Axones, or axis-cylinder pro- 
cesses, i, 39 

B 

Band of Giacomini, 140 
Basal Ganglia, 154, 166, 217 

Arterial supply of, 182 
Basal Lamina, 235 
Base of Brain, 148 

Cerebrum, 147 
Basilar Sinus, 60 
Basis Bundle, 22, 28 
Basis Pedunculi (Crusta or Pes), 

184, 189 

Bechterew's Nucleus, 208, 214 
Blastoderm (^Xaa-ros, a germ ; 

Sep/jLa, skin), 232 
Bodies, Geniculata, 169, 170 

Pacchionian, 53 
Body, Olivary, 78, 80 

Pineal, 161 

Pituitary, 161 

Restiform, 78, in, 122, 221 
Brachia, Corpora Quadri- 
gemina, 190 

Conjunctiva, 109, 186, 221 

Pontis, no, 221 

Brain (see Cerebrum and Ence- 
phalon), 49, 68, 126 

Arteries of, 61 et seq. 

Base of, 148 et seq. 

General outline, 68 

Development of, 238 

Lymphatics of, 66 

Membranes of, 49 et seq. 

Subdivisions of, 49, 68 

Table of Objects on Base of, 
153 



Brain, Veins of, 65, 164 

Brain Sand, 161 

Brocoa's Convolutions, 131 

Area (Olfactory), 132, 141 
Bulb (Olfactory), 132, 198 

Posterior Cornu, 157 
Bundle, Anterior Ground, 22, 28 

Anterior, Median Longitudinal, 
22, 28, 75, 101, 126, 187, 219 

Basis, 22, 28 

Helweg's, 24 

Lateral Ground, 29 

Lowenthal's, 24, 79, 208 

Monakow's, 23, 28, 185, 188 

Olivary, 188 

Posterior Longitudinal, 22, 28, 
75, 101, 126, 187, 220 

Septo-marginal, 29 

Vicq d'Azyr, 176 
Burdach, Fasciculus of, 25, 29, 
77, 89, 228 



Caeruleus, Locus, 98, 103, 122 
Calamus Scriptorius (a writing 

pen), 1 20 
Canal, Central, of Spinal Cord, 

33 (see 232) 
Capsule, External, 168, 178, 224, 

et seq. 

Internal, 168, 178, 224 et seq. 
Cauda Equina (a horse's tail), 6, 

19 

Cavernous Sinuses, 59 
Cells, Antler, 115 
Basket, 114 
Bipolar, 145 
Brain, 144 et seq, 
Cerebellar, 114 
Deiters, 34 
Ependyma, 34 
Fusiform, 145 
Germinal, 234 
Golgi, 146 
Granular, 115 
Horizontal (Cajal), 145 
Molecular Layer of Cerebellum, 

114 
Molecular Layer of Cerebrum, 

144 



INDEX 



247 



Cells, Multipolar, 38, 114 

Nerve Cells, Structure of, 38, 
114, 144 

Neuroblasts, 234 

Neuroglia, 34 

Polygonal, 144 

Polymorphous, 146 

Processes of cerebellum, 115, 
117 

Cerebrum, 145 
Spinal cord, 39 

Purkinje, 115 

Pyramidal, 145 

Root, 40 

Spider, 34 

Spinal Cord, 38 

Spongioblasts, 234 

Structure of, 38, 114, 145 

Triangular, 145 
Central Lobe (Reil), 137 
Centres Cortical of, 

Hearing, 136, 143, 210, 216 

Motor, 133, 142, 222 

Sensory, 133, 142, 177, 216 

Sight, 135, 200, 216 

Smell, 139, 143, 216 

Speech, 131, 142 

Stereognostic, 133, 143, 216 

Summary of Cortical area, 
motor and sensory, 142 

Taste, 136, 143, 216 

Temperature, 133 

Touch, 133 

Vascular supply of, 143 

Vasomotor, 28 
Centrum Ovale, 153 

Majus, 48 

Minus, 47, 153 

Cerebellum (dim. of Cerebrum), 
70,0103, 218 

Cells of, 114 et seq. 

Development of, 232 

Fibres of association, com- 
missural, and projection, 117 
Centrifugal, 118 
Centripetal, 118 

Fissure, Great Horizontal, of, 
107 

Folia of, 1 06 

Functions of, 119 



Cerebellum, Grey Matter of, 113 
Hemispheres of, 104 
Incisura, 105 
Layers of Cells of, 114 
Lobes of, 106 
Medullary Vela of, 112 
Minute Structure of, 114 
Nucleus of, corpus dentatum, 

"3 

Emboliformis, 113 

Fastigii, 113 

Globosus, 113 
Peduncles of, 109 
Position of, 103 
Purkinge's cells, 115 
Vallecula of, 105 
Vermis or Vermiform Process 

of, 105 

White Matter, 116 
Cerebral Hemispheres, 69 
Vesicles, 126, 238 et seq. 
Cerebro-Spinal Fluid, 6, 9, II, 56 
Cerebrum (the brain), 49, 69, 

126 

Arachnoid of, 55 
Arteries of, 61 et seq. 
Base of, 69 et seq., 148 
Commissures of, 154, 171 
Convolutions, of, 130 
Cortex of, 126, 144 
Crura or Pedunculi of, 69, 182 

Constitution, 184 
Development of, 238 
Dissection to remove, 46 
Dura Mater of, 50 
Emissary Veins of, 60 
Fxterior of, 127 
Fissures of, or Sulci, 127 
General Outline of, 126 
Grey Matter of, 127, 144 
Ganglia of, 154, 166 
Hemispheres of, 126, 242 
Interior of, 153 
General Outline of, 153 
Layers of Cells in Cortex, 144 
Lobes of, 130 et seq. 
Membranes of, 50 et seq. 
Peduncles or Crura of, 184 et 
seq. 

Table of, 184 



248 



INDEX 



Cerebrum, Pia Mater of, 54 

Sulci, 127 

Structure of, 144 

Veins of, 65, 164 

Venous Sinuses of, 57 

Ventricles of, 153, 155 

Vessels of, 61 et seq. 

White Matter of, 171 et seq. 
Chiasma optic, 149, 199 
Chorda Tympani, Pars inter- 
media, 206, 207 
Choroid Plexuses, 164 

Fourth Ventricle, 119, 124 

Lateral Ventricle, 155 

Third Ventricle, 159 
Chromatic Matter, 38 
Cinerea, Ala, 125, 211 

Eminentia, 121, 125 

Fasciola, 140 

Lamina, 149 
Cinereum, Tuber, 150 
Cingulum, 177 
Circle of Willis, 64, 66, 148 
Circular Sinus, 59 
Circulation, Special Characters of 

Cerebral, 65 
Clarke's Column, 36 
Claustrum (which shuts off), 168 
Clava (a club), 77, 122 
Cochlear Division (Auditory 
Nerve), 209 
Nucleus, 209 
Collaterals, 30 
Colliculi Anteriores, 190, 217 

Posteriores, 190, 217 
Column or Columns (Funiculi), 18 

Anterior, 21 
Vesicular, 35 

Clarke's (Posterior Vesicular), 
36 

Ganglionic (Motor), 36 

Intermedio-Lateral Tract, 37 

Lateral, 22 
Vesicular, 37 

Middle Vesicular, 37 

Posterior, 25 

Vesicular, 36 

Spinal Cord, 20 

Vesicular, 35 
Table of, 37 



Column or Columns, White 

Anterior, 21 
Lateral, 22 
Posterior, 25 
Columnae fornicis, 176 
Comma Tract, 29 
Commissure (Union), meaning of, 

16 

Great Cerebral (Corpus Callos- 
um), 172 

of Brain, 154, 172 
Anterior, 174 
Middle or Massa Intermedia, 

i?4 

Posterior, 174 
Gudden's, 200 
Spinal Cord, 14, 17 

Grey, 19, 33 

White, 19, 29 
Conus Medullaris, 5, 14 
Convolutions (con, together ; 

volvo, I roll), 130 
Angular, 133 
Broca's, 131 
Central, 130, 137 
Centralis Posterior, 133 
Cerebellum, 103 et seq. 
Cerebrum, 126, 130 et seq. 
Cinguli (Fornicatus), 138 
Corpus Callosum, 138 
Cuneate or Cuneus, 139 
Dentate (Fascia), 140 
Fornicatus (Cinguli), 138 
Frontal (Superior, Middle, and 
Inferior), 131 

Table of, 132 
Hippocampi, 139 
Island of Reil (Central), 137 
Marginal, 139 

Mesial Surface, Table of, 141 
Occipital (Inferior, Middle, 

and Superior), 134 

Table of, 135 

Occipito-Temporal, 136, 140 
Olfactory (Anterior and Pos- 
terior), 132, 141 
Orbital, 131 
Parietal (Inferior and Superior) 

132 

Table of, 134 



INDEX 



249 



Convolutions, Post- Parietal, 133 
Quadrate or Praecuneus, 139 
Rectus, 132 

Supra-Marginal (Turner), 133 
Temporal (Inferior, Middle, 

Superior), 135 
Table of, 136 

Uncinate (Hippocampi), 139 
Cornu Ammonis (from its re- 
semblance to the horns of 
Zeus- Ammon) , Hippocampus 
Major, 158 

Cornua of Lateral Ventricles, 157 
of Spinal Cord, 31 

Lateral, 37 
Corona Radiata, 179 
Corpora Albicantia (Mammil- 

laria,) 150, 153, 175, 176, 241 
Amylacea, 161 
Geniculata (genu, a knee), 170, 

199 
Mammillaria (Albicantia) , 

150, 153- i?5. i? 6 . 2 4* 
Quadrigemina (four), 166, 190, 

239 

Striata, 156, 166, 242 
Corpus Callosum (callosus, thick 

or hard), 69, 126, 156, 172 
Development of, 243 
Dissection to expose, 47 
Genu, 172 
Peduncles of, 172 
Rostrum, 172 
Splenium, 172 
Structure of, 174 
Corpus Dentatum Cerebelli, 113 
Olivi (or Olivary Ganglion), 80 
Pineal, 161 
Restiforme (restis, a rope), 76, 

78, in, 221 
Trapezium, 98 
Trapezoideum, 97, 98 
Cortex of Brain, Structure of, 144 
of Cerebellum, Structure of, 

114 

Corti, Organ of, 209 
Cortical Centres Hearing, 136, 

143, 210, 216 
Motor, 133, 142, 222 
Origins, 197 



Cortical Centres Sensory, 133 

142, 216 

Sight, 135, 200, 216 

Smell, 139, 143, 177, 216 

Speech, 131, 142 

Stereognostic, 133, 143, 216 

Taste, 136, 143, 216, 

Temperature, 133 

Touch, 133 

Summary of Cortical areas, 142 

Vascular supply of, 143 
Cortico-cranial strand, 222 
Cortico-Cerebellar Spinal Strand, 

197, 225 

Cortical Spinal Strand, 223 
Course of Nerve Fibres, Motor 

and Sensory, 27 
Cranial Nerves, 197 

Origins of, 197 

Table of, 152 

Crura ad Cerebrum, ad Medull- 
am, ad Pontem, 109 

Cerebri, 69, 182 

Fornicis, 175 

Crusta Pes, or Basis of Crura 
Cerebri, 182, 189 

Tegmentum, 185 
Cuneate Fasciculus, 77 

Lobe or Cuneus, 139 

Nucleus, 85 

Tubercle, 77 
Cystoplasm, 38 

D 

Decussation (decusso. I cut cross- 
wise), Inferior Pyramidal 
Motor), 71, 74, 75, 88, 223 
Inferior (Sensory), of Spinal 

Cord, 42, 88, 230 
Superior Pyramidal (Sensory), 

41, 88, 230 
Deiters, Cells of, 34 

Nucleus, of, 208, 214 
Dendrones or Dendrites, i, 39 
Dentata Fascia, 140, 158 
Dentate Fissure, 140 
Dentatum Corpus, 86, 113 
Development of Brain, 238 

Spinal Cord, 233 
Diencephalon, 241 



2 5 



INDEX 



Dissection to expose Capsules, 

49 

Corpus Callosum, 47 

Crura cerebri, 49 

Fornix, 48 

Interior of Brain, 48 

Lateral Ventricles, 48 

Medulla, 70 

Membranes of Brain, 46 

Pia Mater, Spinal Cord of, 7 

Septum Lucidum, 48 

Spinal Cord, 4 

Spinal Vessels, 1 1 

Velum Interpositum, 49 

3rd Ventricle, 49 

5th Ventricle, 48 

Vessels of Brain, 61 

White Matter of Pons, 98 
Dissection to remove Brain, 46 

Cochlear Nucleus, 209, 213 

Nucleus (Clarke's Column), 36 

Vestibular Nucleus, 208, 214 
Dura Mater of Brain, 50 

Structure of, 53 

Spinal Cord, 5 

Structure of, 6 



Ectoderm, 232 
Emboliformis, Nucleus, 113 
Eminentia Cinerea, 121, 125 

Collateralis, 158 

Saccularis, 150 

Teres, 121, 122, 205 
Emissary Veins, 60 
Encephalon (eV in ; xe^aXi?, the 

head) (see Cerebrum), 49 
Enlargements, Cervical, 15 

Lumbar, 15 
Entoderm, 232 

Ependyma (ti>8v/jia., clothing) 
of Cells, 34, 158, 233 

of Spinal Cord, 34 

of Ventricles, 34, 158 
Epiphysis Cerebri, 242 



Facial Nerve (7th), 205 
Falx Cerebelli, 52 
Cerebri, 52 



Fascia Dentata, 140, 158 
Fasciculus or Fasciculi Ascend- 
ing antero-lateral (Gowers) , 
23, 28, 89, 100, 229 

Ascending spino - cerebellar, 
dorsalis, or posterior, 23, 
. 79, 89 

Ascending spino - cerebellar, 
ventralis, or anterior, 23, 
28 

Bulbo-thalamic, 90, 99 

Burdach or Cuneati, 25, 41, 77 

Cerebro-Spinal Anterior or 
Direct Pyramidal Tract, 
or Tiirck, 21, 74 

Cerebro - Spinalis Lateralis, 
or Crossed Pyramidal, 22, 
74, 78, 223 

Crossed Pyramidal, 22, 74, 78 

Cuneatus, 25, 77 

Descending Anterio-lateral, 24, 

79 
Descending Cerebello-Spinalis, 

Anterior, or Ventralis 

Lowenthal, 24 
Direct Cerebellar, 23 
Direct Pyramidal, 21, 74, 224 
Geniculate, 189 
Gracilis or Goll, 25, 76 
Helweg, 24 
Lowenthal, 24, 79 
Lateral Cerebellar, 23, 28, 42, 

79, 229 
Lateral Division of Anterior 

Column, 22 
Lateralis, 189 

Marginal Zone, Lissaeurs' 26 
Medulla, 73 

Monakow, 23, 28, 185, 188 
Olivo-Spinal, Helweg, 24, 79 
Olivary, 102, 188 
Pallidal, 226 
Postero-Marginal, 26 
Prepyramidal or Rubro-spinal, 

Monakow, 23, 79, 101, 188 
Proprius Anterior, 22, 74, 75 
Lateralis, 25 
Posterior, 26 
Rolando, 77 
Rubro-Spinal, 23, 79, 101, 188 



INDEX 



251 



Fasciculus or Fasciculi Spinal 

Cord, 21-25 
Table, 28 
Spino-Cerebellar Posterior, or 

dorsalis, 23, 79, 89 
Spino-Tectal, 24, 79, 89, 101, 

188 
Spino-Thalamic, 24, 79, 89, 90, 

99, 100, 188, 229 
Solitarius, 94, 210, 211 
Strio-Spinal or Pallidal, 226 
Teres, 102, 122, 124, 205, 212 
Table of Fasciculi, 28 
Tiirck, 21, 74 

Ventro-Spino-Cerebellar, 24 
Vestibulo-Spinal, 24 
Fasciola Cinerea, 140, 173 
Fastigii, Nucleus, 113 
Fibres, Association, 116, 171, 

175, 178, 219 
Table of, 178 
Arcuate, or Arciform, 72, 73, 

80, 91 

Commissural, 116, 171 
Longitudinal, of Pons and 

Crura, 99, 186 
Moss, 117 
Projection, 106, 158, 164, 171, 

195 

Transverse, of Pons and Crura, 

98, 189 
Fifth Nerves, 204 

Ventricle, 162 
Fillet (Lemniscus), 77, 89, 90, 99, 

100, 1 86, 229 

Lateral, 99, 100, 187, 191, 230 
Mesial, or Main, 77, 89, 90, 99, 

100, 229 
Superior, 230 
Filum Terminate, 6, 9, 15 
Fimbria, (a fringe) 140, 158, 175 
Fissures, or Sulci, 

Anterior Median of Spinal Cord 

16 
Antcro-lateral, 17 

( ';ilr;irinc. I .;. i 

Callosal, 138 
Calloso-Marginal (Sulcus Cin- 

guli), 129, 138 
Cerebri Centralis, 128 



Fissures, Lateralis (Sylvius), 128 

Cerebrum, 127 et seq. 

Collateral, 1-40 

Dentate, 140 

Great Horizontal, 107 

Great Longitudinal, 69 

Great Transverse, 158, 165 

Hippocampi, 140 

Inter-Lobular, 128 

Intra-Lobular, 129 

Intra-Parietal, 133 

Lateral, of Spinal Cord, 17 

Longitudinal, Great, or Inter- 
Hemispherical, 69, 126 

Median, of Spinal Cord, 16 

Medulla, 72 

Anterior Median of, 72 
Lateral of, 73 
Posterior Median of, 72 

Mesial Surface of Brain, 192 

Praecentral, 131 

Parallel, 124 

Parieto-Occipital, 129, 132, 

134. J 39 

Postero-Median, 17 
Postero-Lateral, 17 
Rolando, 128, 130, 132 
Spinal Cord, 16, 237 
Sylvius, 128 

Transverse, Great, 158, 165 
Triradiate, 131 
Flechsig's Tract, 28 
Flexures, Cranial, 240 
Flocculus (dim. of floccus, a flock 

of wool,) 107 

Floor of 4th Ventricle, 120 
Fluid, Cerebro-Spinal, 6, 9, n, 56 
Folia of Cerebellum, 106 
Foramen Caecum of Medulla, 72, 

of Majendie, 56, 122, 123 
Foramina Interventricularia 
(Monro), 159, 160, 164, 176, 
242 
Forceps Major, 157, 172 

Minor, 172 
Formatio Reticularis, 84, 85, 03, 

102 
Fornix (an arch or vault), 150, 

156, 160, 175, 243 
Dissection to expose, 48 



252 



INDEX 



Fourth Nerves, 203 
Ventricle, 119 et seq. 
Choroid Plexus of, 124 
Ependyma of, 123 
Floor or Anterior Wall of, 

1 20 

Grey Matter of, 124 
Lateral Walls of, 122 
Nulcei of, 124 
Openings into, 123 
Roof of, 122 
White Matter of, 125 
Fovea (a pit), Inferior, 121 

Superior, 122 

Functions of Cerebellum, 1 19 
Funiculus Anterior, 21. (See 

Column and Fasciculus) 
Lateralis, 22 
Posterior, 25 
Furrowed Band, 108 



Galen, Vein of, 59, 65, 164 
Ganglia, 

Basal (sub-cortical), 126, 154, 
1 66, 217 

Cortical, 126, 142, 215 

Spinal, 19. 41 

Sub-Cortical, 126, 166 
Ganglion, Gasserian, 204, 207 

Geniculate, 207 

Meckel's, 207 

Scarpa's, 208 

Spiral Ganglia, 209 

Vestibular, 208 
Ganglionic (Vesicular) Columns 

of the Spinal Cord, 35 
Gasserian Ganglion, 204 
Gelatinosa, Substantia, 32, 34, 

.4 1 . !3 
Geniculate Bodies, Inner and 

Outer, 169, 170, 199 
Genu (Knee) of Corpus Callosum, 

172 

of Internal Capsule, 179 
Germinal Membrane, 232 
Giacomini, Band of, 140 
Gland, Pineal, 161 
Glandulae Pacchionii, 53 
Globosus, Nucleus, 113 



Globus Pallidus, 167 
Glosso-Pharyngeal Nerve, 210 
Golgi, Cells of, 146 
Goll, Fasciculus or Tract of, 25, 

76, 228 
! Gowers, Fasciculus or Tract of, 

23, 28, 79, loo, 229 
Gowers' Table, 45 
Granular Layer of Cerebellum, 

H5 

Great Transverse Fissure, 165 
Grey Commissure, 33 
Grey Matter of Cerebellum, 115 

Cerebrum, 127, 144 

Medulla, 83 
Table of, 82 

Pons Varolii, 102 

Spinal Cord, 19, 31, 33, 236 
Constitu tents of, 33, 35 

Tegmentum, 97 185, 
Groove, Antero-Lateral, 17 

Oculo-Motor, 183, 20 1 

Olfactory, 132, 198 

Postero-Lateral, 17 

Prinitive, Neural, 232 
Gudden, Commissure, 200 
Gyri (71^6$, a circle) of Brain (see 
Convolutions), 130 et seq. 

Operti, 137 
Gyrus, Angular, 133 

Cinguli, 138 

Fornicatus (Arched) or Cinguli, 
138 

Hippocampi, 139 

Rectus, 132 

Uncinate, 139 

H 
Hemispheres, Cerebral, 69, 127, 

242 

Herophili, Torcular, 57 
Hippocampal Convolution or 

Gyrus, 139, 140 
Fissure or Sulcus, 140 
Pes, 158 
Taenia or Fimbria, 140, 141, 

158 

Hippocampus (after a fish of that 
name) Major, Cornu Am- 
moiiis, 158 



INDEX 



253 



Hippocampus Minor, 157 
Horns of Spinal Cord, 31, 32, 37 

Lateral Ventricles, 157 
Hypoglossal Nerve, 212 
Hypoglossi Trigonum, 124, 212 
Hypophysis Cerebri (Pituitary 
Body), 150, 161 



Incisura Cerebelli, Posterior, 105 
Infundibulum (Funnel), 150, 159 

242 

Insula or Island of Reil, 137 
Interior of Cerebrum, 153 
General Outline, of 153 
Inter-Lobular Fissures or Sulci, 

129 

Interpeduncular Space, 148 
Interpositum, Velum, 163 
Interventricularia Foramina 

(Monro), 154, 159, 160, 176, 

242 

Intra-Lobular Fissures, 128 
Isthmus of the Convolution of the 

Corpus Callosum, 138 
Rhombencephali, 240 



Lamina Alar, 235 
Basal, 235 

Cinerea (Grey Layer), 149 
Quadrigemina, 190, 191 
Terminalis, 149, 160, 172, 242 
Lancisi, Nerves of, 173 
Lateral Recess of 4th Ventricle, 

120 

Lateral Ventricles, 155, 242 
Lcmniscus or Fillet, 89, 93, 99, 

187, 229 et seq. 
Lenticularis, Nucleus, 167 
Ligamentum Denticulatum, 8 
Ligula (dim. of Lingula) or 

Taenia, 123 
Limen Insulae, 137 
Linea Splendens, 8 
Lingula (Tongue) Cerebelli, 107, 

112 

Lissauer's Tract, 26, 29, 41 
Lobes (see Convolutions), Central 
(Reil), 137 



1 Lobes, Cerebellum, 106 

Cerebrum, 130 

Frontal, 130 

Limbic, 139, 141 

Occipital, 134 

Olfactory, 132 

Parietal, 132 

Temporal, 135 
Lobules Cerebrum, 130 

Cuneate, 139 

Fusiform, 140 

Lingual, 140 

Paracentral, 139 

Parietal, 132 

Praecuneus, 139 

Quadrate, 107, 139 
Lobulus Centralis, 137 
Locomotor Ataxy, 26 
Locus Caeruleus, 103, 122 

Niger, 184, 190 

Perforatus Anticus, 150 

Perforatus Posticus, 150 
Longitudinal Bundles, 219 
Longitudinal Fibres, 99, 186 
Lowenthal's Bundle, 24, 79 
Lymphatics, Brain, 66 

Spinal Cord, 13 
Lyra (a lute) Psalterium, 177 

M 

Majendie, Foramen of, 56 
Mammillaria Corpora, 122, 123, 

150, 153, 175, 176, 241 
Mantle, or Pallium, 127, 243 
Mantle Layer, 234 
Marginal Zone, Lissauer's, 26 
Massa Intermedia, 174 
Matter, Grey Cerebellum, 113, 
114 

Cerebrum, 127, 144 

Medulla, 83 

Pons Varolii, 102 

Spinal Cord, 31, 236 

Tegmentum, 185 
White Cerebellum, 116 

Cerebrum, 171 

Fourth Ventricle, 119, 125 

Medulla, 73 et seq. 

Spinal Cord, 20 

Tegmentum, 186 



254 



INDEX 



Meckel's Ganglion, 207 
Medulla Oblongata, 70 et seq. 
Anterior Area of, 73 
Anterior Columns of, 73 
Arcuate Fibres, 91 
Development of, 240 
External Characters of, 70 
Fissures of, 72 
Fasciculi, 76, 77, 78 
Formatio Reticularis, 85 
Grey Matter of, 83 
Isolated Nuclei of, 86 
Lateral Area or Columns of, 

78 
Nucleus Cuneatus, 85 

Gracilis, 85 

Lateralis, 84 

Rolando, 85 

Cranial Nerves, 87 
Posterior Area or Columns, of, 

75 
Pyramids, Areas or Columns 

of, 73 et seq. 
Raph6 of, 87 
Recapitulation, 92 
Summary, 81 
Surface, Table of Objects on, 

81 

Spinal Medulla, 1 4 
White Matter, of 73 
Medullares, Striae, 71, 120 
Medullary Cone, 5 
Vellum, 112, 123 
Inferior (Valves of Tarini), 112 
Superior (Valve of Vieussens), 

105, 112, 123 
Membranes of Brain, 49 et seq. 

Spinal Cord, 4 et seq. 
Meninges (/tjjwyf, a membrane), 

2, 49 et seq. 
Dissection for, 46 
Mesencephalon (/n&roj, middle ; 
tvKt<t>a\ov, the brain), 239, 
240 

Mesoderm, 232 
Metencephalon, 240 
Minute Structure (see Structure) . 
Mixed Zone, 25 

Monakow's Bundle (Prepyra- 
midal), 23, 79, 101, 188 



Monro, Foramina 159, 160, 

164, 176, 242 
Montiulus Cerebelli, 108 
Motor Centre, 133, 216 
Impulses, 27 
Strands or Tracts, 20, 73, 74, 

99, 1 86, 219 et seq. 
Myelencephalon, 240 
Myelospongium, 234 

N 

Nerves Cranial, 152, 197 et seq. 
Origins, Cortical, Deep or 

Sub-cortical, 197 
Superficial, 151, 197 
Fibres, White Structure, 30 
Roots, Spinal, 18, 40 

Cranial, 197 
Spinal, 1 8 

Anterior (Motor), 19 
Posterior (Sensory), 19 
Origins, Deep, 40 
Superficial, 40 
Table of, Cranial 152 
Nerve Cells Processes of, 39, 

"7. 145 

Structure of, 38, 114, 144 

Cerebellum, 114 

Cerebrum, 144 et seq. 

Spinal Cord, 38 
Nervous System, Table of, 2 
Neural Groove, 232 

Crest, 233 

Tube, 232 
Neuroblasts, 234 
Neuroglia (veupov, nerve; y\ia, 
glue), i, 14, 34, 147 

Cells, 34 

Fibres, 34 

Neurones, i, 35, 215 
Niger, Locus, Substantia Nigra, 

184, 190 

Nissl's Granules, 38 
Nodule of Cerebellum (Lamin- 
ated Tubercle), 108 
Nulcei of Arciform or Arcuate 
Fibres, 87 

Cerebelli, 113 

Cranial Nerves, 124, 197 

Fourth Ventricle, 124 



INDEX 



255 



Nulcei of Medulla, 84 

Origin of Nerves Cranial, 124 
197 

Spinal, 40 
Tecti, 113 

Third Nerve, Table of, 203 
Nucleus Accessory and Super- 
ior Olivary, 98, 103 

Cochlear, 209 
Ambiguus, 210, 211 
Amygdalae, 158 
Arciform, 87 
Bechterew, 208, 214 
Caudatus, 166 
Cuneatus, 85 
Deiters, 208, 214 
Dorsal (Clarke's Column), 36 
Dorsal Cochlear, 209 

Vestibular, 209 
Emboliformis, 113 
Fastigii, 113 
Globosus, 113 
Gracilis, 85 

Intermedio-Lateral Tract, 37 
Lateralis of Medulla, 84 
Lenticularis, 167 
of Nerves Auditory, 124, 125, 
207 

Fifth, 125, 204 

Fourth, 125, 203 

Glosso-pharyngeal, 125, 210 

Hypoglossal, 124, 212 

Olfactory, 197 

Optic, 199 

Seventh, 125, 205 

Sixth, 125, 205 

Spinal Accessory, 125, 211 

Third, 201 
Table of, 203 

Vagus, 125, 211 
Oculomotor, 201 
Olivary Body (Corpus Denta- 
tum, 80, 93, 98 

Accessory Olive, 86, 93 

Inferior Olivary, 80 

Superior Olivary, 103 
Optic Thalamus, 168 
Pontis, 103 

Ki-d (Tegmenti), 185, 217, 221 
Kolando, 85 



Nucleus Superior Olivary, 103 
Tegmenti (Red), 185, 217, 221 
Ventral Cochlear, 209 
Vestibular, (Scarpa's Gang- 
lion), 208 

O 

Obex (a bar), 122 

Objects on Base of Brain, Table 

of, 148, 153 
Objects on Surface of Medulla, 

Table of, 81 
Occipital Sinuses, 60 
Oculomotor Grooves, 183, 201 
Olfactory Area (Broca), 132, 141 
Brain, 141 
Bulb, 132, 198 
Groove, 132 
Lobe, 132, 197 
Nerves, 197 
Peduncles, 132, 197 
Trigonum, 141, 199 
Tubercle, 141, 199 
Olivary Body (Olivia, an olive), 

71, 80 
Bundle, 188 
Corpus Dentatum, 80 
Nucleus, 86, 93, (Corpus Den- 
tatum) 

Inferior Olivary, 71, 80 
Superior Olivary, 98, 103 
Peduncle, 86, 93 
Olives, Accessory, 86, 93. 98 
Openings into 4th Ventricle, 123 
Operculum (covering or lid) of 

Insula, 137 
Operti, Gyri, 137 
Optic Chiasma or Commissure, 

M9, 153. 199 

Nerves, 199 

Radiation, 180, 200 

Stalks, 241 

Thalamus, 154, 156, 160, 168 

Tract, 150, 183, 199 

Vesicles, 241 

Orbitalis (Triradiate) Sulcus, 131 
Origins of Nerves, Cranial, 151, 

197 et seq. 

Spinal, 40, et seq. 



'56 



INDEX 



Pacchionian Bodies, 53 
Pain, Sense of, 28 
Pallidal System, 226 
Pallium or Mantle, 127, 243 
Paracentral Lobule, 139, 216 
Paramedian Sulcus, 18, 72 
Parasinoidal Spaces, 58 
Parieto-Occipital Sulci, 129, 134, 

139 

Pars Frontalis of Internal Cap- 
sule, 179 

Intermedia (7th Nerve), 206 
Occipitalis, 179 
Opercularis, 131 
Orbitalis. 131 
Triangularis, 131 
Peduncle, Olivary, 86 
Peduncles of Cerebellum, 104, 

109, 221 

Cerebrum, 69, 126, 182 et seq. 
Corpus Callosum, 172 
Pineal Gland, 160, 161 
Perforated Spot, Anterior, 150 
Posterior (Pons Tarini), 150 
Pes, Crusta, or Basis of Crura 

Cerebri, 189 
Pia- Arachnoid, n, 55 
Pia Mater of Brain, 54 
Spinal Cord, 7 
Dissection, 7 
Septa, 7, 8, 9 
Structure of, 9, 55 
Pillars, Fornix, 175 
Pineal (Pinea, a pine-cone) Body 

or Gland, 161, 242 
Pituitary (Pituita, phlegm or 
mucous) Body, 150, 161, 
242 
Plexus, Choroid, 124, 156, 160, 

164 
Pons Tarini (Posterior Perforated 

Spot), 150 

Pons Varolii, 70, 95, 240 etseq. 
Constitution of, 97 
Formatio Reticularis of, 99, 

1 02 

Grey Matter of, 102 
Nucleus of, 103 
Raph6 of, 102 



Pons Varolii, Table of, 97 
White Matter of, 98 et seq. 
Longitudinal Fibres, 99 
Transverse Fibres, 98 

Posterior Median Sulci, 17, 72 

Posterior Perforated Spot, 150 

Prsecentral Sulci, 131 

Praecuneus or Quadrate Lobe, 

139 
Prepyramidal Tract, 23, 79, 80, 

101, 227 

Primary Cerebral Vesicles, 238 
Primitive Neural Groove, 232 

Tube, 232 

Principal Motor Strands, 223 
Processes Axis Cylinder, 39, 

117, 145, 228 
Collateral, 30, 145 
Protoplasmic, 39, 146, 228 
Reticularis, 32 

Projection Fibres, 117, 171, 219 
Proscencephalon (717)65, before ; 
fv, in ; Ke<f>a\r), the head), 
241 

Psalterium (Lyra) Fornicis, 177 
Pulvinar (a couch), 169, 199 
Purkinje, Cells of, 115, 117 
Putamen, 167 
Pyramidal Tracts of Medulla, 74, 

78, 79, 88 
Crura Cerebri, 189 
Spinal Cord, 21, 22, 23 
Crossed, 22, 23 
Direct, 21, 22, 23 
Uncrossed Lateral, 23 
Pyramid of Cerebellum, 108 
Pyramids of Medulla Areas or 

Columns, 73 
Anterior, 73 
Lateral, 78 
Posterior, 75 
Decussations, Inferior (Motor), 

74, 88, 223 

Superior (Sensory) Fillet, 77, 
88, 93, 228 

Q 
Quadrate Lobe (Cerebelli), 107 

(Prsecuneus) (Cerebri), 139 
Quadrigemina, Corpora, 190, 217 



INDEX 



257 



R 



Radiata Corona, 179 
Radiation Auditory, 180, 210 

Optic, 1 80, 200 
Ranvier Nodes, 30 
Raphe (f>cuj>r), a seam) of Corpus 

Callosum, 173 
MeduUa, 87 
Pons, 102 
Realms, Trophic (Wyllie's), 36, 

223 
Recapitulation of Medulla, 92 et 

seq. 

Recesses, Lateral, 120 
Red Nucleus, 185, 217, 221 
Reil, Island of, 137 
Relations of White Tracts in Cord 

and Medulla, Table of, 82 
Restiform (Restis, a rope), Bodies 

76, 78, in, 221 
Reticularis, Formatio, 84, 85, 93, 

1 02 

Rhinencephalon, 141 
Rhombencephalon, 240 
Rolando, Fasciculus of, 76, 77 
Fissure of, 128 
Nucleus of, 85 
Substantia Gelatinosa of, 32, 

34, 41, 103 
Tubercle of, 77, 94 
Roof of 4th Ventricle, 122 
Root Zone, 22 

Spinal, of 5th Nerve, 94, 205 
Rostrum of Corpus Callosum, 

148, 172 

Rubro-Spinal Tract (Prepyra- 
midal), Monakow's Bundle, 
23, 79, 80, 101, 1 88, 227 
Rust-Coloured Layer of Cere- 
bellum, 115 



Saccularis Eminentia, 150, 159 

Sagittal Sinuses (Superior and In- 
ferior), 57, 58 

Scarpa's Ganglion, 208 

Secondary Cerebral Vesicles, 238 
et seq. 

Segments, Spinal, 15 



Senses Hearing, 136, 180, 209, 
230 

Muscular, 26, 27, 180 

Pain, 28, 1 80 

Sight, 143, 180, 200, 216 

Smell, 143, 199, 216 

Taste, 143, 207, 216 

Temperature, 28, 180 

Touch, 28, 1 80 

Sensory Decussation, 43, 85, 88, 
93, 228 

Impulses, 27 
Septum Lucidum, 162, 173, 244 

Posticum of Spinal Cord, 9 
Sinuses Basilar or Transverse, 
60 

Cavernous, 59 

Circular, 59 

Lateral, 58 

Longitudinal, Inferior (Sagit- 
tal), 58 
Superior (Sagittal), 57 

Occipital, 60 

Petrosal Inferior, 60 
Superior, 60 

Spheno-Parietal, 60 

Straight (Rectus), 59 

Transverse or Basilar, 60 

Venous, 51, 57 et seq. 
Sixth Nerve, 205 
Spaces Interpeduncular, 148, 

153 

Perforated, Anterior, 150 

Posterior, 150 

Sub-Arachnoid, 5, 10, 56 

Sub-Dural, 5, 10, 56 
Speech Centre, 131, 142 
Spheno-Parietal Sinuses, 60 
Spinal Accessory Nerves, 211 
Spinal Arteries, n 

Lymphatics, 13 

Nerves, 18 

Veins, 13 
Spinal Cord, 14 

Arachnoid of, 9 

Arteries of, 1 1 et seq. 

Central Canal of, 33, 232 

Columns or Funiculi of, 20 et 

seq. (See Table, page 28) 
Vesicular, 35 et seq. 

s 



INDEX 



Spinal Cord, Commissures, Grey, 

19, 33 
White, 19, 29 

Cornua of, 31 

Development of, 233 

Divisions of, 15 

Dura Mater of, 5 

Enlargements of, 15 

External Form of, 14 

Fasiculi of (see Fasiculus), 20 
et seq. 

Filum Terminale of, 9, 15 

Fissures of, 16 et seq. 

Grey Matter of, 19, 31 
Structure of, 33 

Ligamentum Denticulatum, 8 

Lymphatics of, 13 

Membranes of, 4 ef^seq. 

Nerves, 18 

Nervous Constituents of, 35 

Neuroglia of, 4 

Origins of Spinal Nerves, 40 

Parts of, 15 

Pia Mater of, 7 

Segments, 15 

Tracts or Strands of, 20 et seq. 

Veins of, 13 

Vesicular Columns of, 35 et seq. 

White Matter of, 19, 20 

Structure of, 30 
Spino-Tectal Tract, 24, 28, 79, 

101, 188, 227 
Spino-Thalamic Tract, 24, 28, 79, 

loi, 188, 229 

Splenium (ffirXyi'lov, a compress) 
of the Corpus Callosum, 172 
Spongioblasts, 234 
Spots, Perforated, 150 
Straight Sinuses, 59 
Strands (see Tracts), Long, 222 

Motor, 75, 179, 222 

Cortical Motor, 222 

Sensory, 180, 227 

Short, 219 

Subcortical Motor, 226 

White, 171 
Stratum Griseum, 185 

Intermedium, 189 
Striae Acusticae (Medullares), 71, 
120 



Striae Acusticae, Longitudinal, 
Lateral, and Mes:al, of 
Corpus Callosum, 173 
Terminalis, 169, 177 
Striata, Corpora, 154, 166, 242 
Strio-Spinal Motor System, 226 
Structure (Minute) of Arachnoid 

of Brain, 55 
of Spinal Cord, 1 1 
Dura Mater of Brain, 53 

of Spinal Cord, 6 
Grey Matter of Cerebellum, 

114 

of Cerebrum, 144 
of Spinal Cord, 33 
Nerve Cells, 38, 114, 144 
Optic Thalami, 170 
Pia Mater of Brain, 54 

of Spinal Cord, 9 
White Matter of Spinal Cord, 

30 

Sub-Arachnoid Fluid, u, 56 
Space, 10, 56 
Trabeculae, 9, 10, 55 
Sub-Cortical Origins, 197 

Ganglia, 217 
Subdivisions of the Brain, 68, et 

seq. 

Sub-Dural Space, 5, 10, 56 
Substantia Gelantinosa, 32, 34, 

103 

Nigra, 184, 190 
Sulci (see Fissures), 127 
Calcarine, 139 
Callosal, 138 

Calloso-Marginal (Cinguli), 138 
Centralis (Rolando), 128 
Centralis Insular, 137 
Cerebral, 127 et seq. 
Cerebri Lateralis (Sylvius), 128 
Cinguli, 138, 139 
Collateral, 140 
Dentate, 140 
Frontal, 131 
Inferior Temporal, 135 
Inter- Lobular, 128 
Intra-Lobular, 129 
Intra-Parietal, 133 
Island of Reil, 137 
Lateral (Crus Cerebri), 183 



INDEX 



259 



Sulci, Lateral Dorsal, 18, 72, 77 

Lunatus, 135 

Middle Temporal, 135 

Oculomotor, 183, 201 

Olfactory, 132 

Orbitalis, 131 

Paramedian, 18, 72, 77 

Parieto-Occipital, 129, 132, 139 

Posterior Median, 72 

Praecentral, 131 

Sub-Parietal, 138 

Temporalis, 135 

Triradiate, 131 
Summaries, Cerebrum Mesial 

Section, 192 
Ventricles, 194 

Decussations, go 

General, 215 et seq. 

Medulla, 81, 92 

Spinal cord, 43 

Tracts, 27, 28" 

Vascular Supply of Cortex, 143 
Superficial, Origins of Cranial 
Nerves, 151 

Spinal Nerves, 18 
Surface, Mesial Brain, 192 

Hemispheres, ig7 
Sylvius, Aqueduct of, 123, 154, 
160, 191, 239, 241 

Fissure, 128 
Sympathetic System, i 
Synapses or Plexus, 31 
Syncytium, 233 



Tables Association Fibres, 178 

Cerebral Arteries, 67 

Cerebral Vesicles, 239 

Convolutions, Frontal, 132 
Mesial Surface, 137 
Occipital Lobe, 134 
Parietal Lobe, 132 
Temporal Lobe, 135 

Cranial Nerves, 152 

Fissures, Inter-Lobular, 129 

Cowers', 45 

Grey Matter of Medulla, 87 

Nervous System, 2 

Nuclei of Third Nerve, 203 

Objects on Base of Brain, 153 



Tables Objects on Surface of 

Medulla, 81 
Order in which Tracts get their 

Medullary Sheath, 43 
Pedunculi Cerebri, 184 
Pons Varloii (White and Grey 

Matter), 97 
Relations of Tracts of Cord 

and Medulla, 82 
Sensations, Kind of, 44 
Sulci, 129 

Vesicular Columns, 35 
White Tracts of Spinal Cord, 28 
Taenia (raivia, a'band), or Ligula 

123 
Hippocampi, or Fimbria, 158, 

i?5 

Semicircularis, or Stria Ter- 
minalis, 156, 158, 169, 177 

Tarini Pons, or Posterior Per- 
forated Spot, 150 
Valves of (Inferior Medullary 
Velum), 112 

Taste, Sense of, 143, 207, 216 

Tecto-Spinal Tract (Ventral 
Bundle), 22, 75, 101, 187 

Tegmentum (covering) of Crura 
Cerebri, 185 
Pontis, 97 
Nucleus (Red), 185, 217, 221 

Tela Choroidea Inferior, 55, 124 

Telencephalon, 242 

Temperature, Sense of, 28, 44, 180 

Temporal Lobe, 135 

Tentorium (a tent) Cerebelli, 52 

Teres Eminentia, 122, 124, 205 
Fasciculus, 102, 122, 124, 205 

Terminale, Filum, 6, 9, 15 

Thalamus (bed-chamber) Opticus 
154, 156, 160, 168 

Third Nerves, 201 

Third Ventricle, 159 

Tonsilla (Amygdaloid Lobe), 107 

Torcular Herophili, 57 

Touch, Sense of, 28, 180, 228 

Trabeculae Sub- Arachnoid, 9, II 

Tracts (see Fasciculi, also Tables) 
Anterior Ground Tract, Fasci- 
culus Proprius Anterior, 22, 
28, 74, 75 



260 



INDEX 



Tracts, Antero-Lateral Ascending 
(Cowers 1 ), 23, 28, 42, 79, 80, 

82, 89, 97, 100, 228, 229 
Antero - Lateral Descending 
(Lowenthal) vestibulo-spinal 

24, 29, 79, 82, 227 
Anterior Root Zone, 22 
Ascending Antero - Lateral 
(Gowers') 23, 28, 42, 79, 80, 

82, 89, 97, 100, 228, 229 
Basis Bundle, 22 
Bulbo-Thalamic, 90. 99 
Burdach, 25, 29, 41, 77, 89, 

228 
Cerebro-Spinalis anterior, 2 1 , 

28, 74, 88, 97, 224 
Cerebro-Spinalis Lateralis, 22, 

28, 74, 88, 97, 224 
Caudate - cerebellar, (Stratum 

Intermedian} , 185, 189 
Corti co-Cranial, 222 
Cortico-Cerebellar Spinal, 225 
Cortico-Motor, 222 
Cortico-Pontine, 97, 99, 189 
Cortico-Spinal, 223 
Crossed Pyramidal, 22, 74, 88, 

97. 223 

Cuneate, 25, 29, 77 
Descending Antero - Lateral 

(Lowenthal, Vestibulo- 

Spinal), 24, 29, 79 
Descending Cerebello-Spinalis 

ventralis (Lowenthal), 24 
Direct Cerebellar, Direct 

lateral Cerebellar (Flechsig), 

Spino - Cerebellar Dorsalis, 

23, 28, 42, 79 

Direct Pyramidal, Cerebro- 
Spinalis Anterior, 21, 74, 88, 

97, 224 
Dorso-Spino -Cerebellar (Lateral 

Cerebellar), 23, 42, 79, 80, 88, 

229 
Fillet, 90, 97, 99, 100, 186, 229, 

230 

Flechsig, 28 
Fronto-Pontine, 185 
Geniculate, 189 
Goll, 25, 29, 41, 76, 228 
Gracilis, 25, .29, 76 



Tracts, Gowers', 24, 28, 79, 100, 

229 

Helweg, 24, 25, 29, 78, 79 
Lateral Cerebellar, 23, 42, 79, 

80, 88, 229 
Lissauers' (Postero-Marginal), 

26, 29, 41 

Lowenthal, 24, 29, 79, 80, 227 
Mixed Zone, 25 
Motor Tracts or Strands, 27, 88 

Principal Motor Strand, 223 

Secondary Motor Strand, 

225 
Olivo-Spinal (Helweg), 24, 25, 

7 8 . 79 

Ponto-Spinal, 227 
Postero-Marginal (Lissauers'), 

26 
Proprius Anterior, 22, 28, 74, 

75 

Proprias Lateralis, 25, 80 
Proprius Posterior, 26 
Prepyramidal, Rubro-Spinal, 

Monakow, 23, 79, 80, 101, 

188, 227 
Pyramidal, Crossed, 22, 27, 74, 

78,97 

Direct, 21, 27, 74, 97 

Uncrossed, 23, 27, 74, 97 
Pyramidal of Spinal Cord, 21, 
22, 23 

Medulla, 73 

Peduncles, orTCrura Cerebri, 
185, 189 

Pons, 97, 99 
Rolando, 76, 77 
Rubro-Spinal, Prepyramidal, 

Monakow, 23, '79, 101, 188, 

227 
Sensory Tracts, or Strands, 27, 

88, 222, 227 
Spino-Cerebellar Ventralis 

(Gowers'), 24 

Spino-Cerebellar Dorsalis, 23^ 
Spino-Tectal, 24, 79, 88, 89, 90, 

97, 101, 229 
Spino-Thalamic, 24, 79, 88/89, 

90, 97, 100, loi, 229 
Strio-Spinal, 227 
Stratum Intermedian, 185, 189 



INDEX 



261 



Tracts, Sub - Cortical Motor 

Strands, 226 

Tecto-Spinal, 101, 219, 227 
Temporo-Pontine, 189 
Table of Tract of Spinal Cord, 

28 

ot Medulla, 82 
Tiirck, 21 
Uncrossed Lateral Pyramidal, 

23, 74, 78. 224 

V e n t r o - Spino - Cerebellar 
(Gowers), 24, 79, 88, 100, 
229 

Vestibulo-Spinal (Lowenthal), 

24, 25, 227 
Transverse Fibres of Pons, 98 

of Crura, 189 
Fissure, Great Transverse, 54, 

158, 165 

Trapezium or Corpus Trapezo- 
ideum of Pons Varolii, 98, 
210 
Trigonum Acusticum, 121, 124, 

209 

Hypoglossi, 121, 124, 212 
Olfactorium, 141 
Vagi, 121 
Trophic Realms (Wyllie's), 36, 

39, 223 

Tuber Cinereum, 150, 159 
Valvulae or Vermis, 108 
Tubercle Amygdaloid, 107 
Acoustic, 124, 209 
Cuneate, 77 
Olfactory, 141, 199 
Rolando, 77, 78, 94 
Tuberculum Acusticum, 121, 209 
Tiirck, Fasciculus of, 21 
Tympani, Chorda, 207 

U 
Uncinate or Hippocampal Gyrus, 

139 

Uncus Gyn Hippocampi, 139 
Uvula (dim. of uva, a cluster of 

grapes) of Cerebellum, 108 



Vagus Nerve, 211 
Vallecula of Cerebellum, 105 



Valve of Vieussens, 105, 109, 112 
Valves of Tarini, 150 
Varolii, Pons, et seq. 95 
Vascular Supply of Cortical 

Centres, 143 
Vasomotor Impulses, 28 
Veins, Cerebellar, 65 
Cerebral, 65, 164 
Emissary, 60 
of Galen, 59, 65, 164 
Spinal, 13 
Velum, Inferior or Posterior 

Medullary, 105, 109, 112 
Tnterpositum, 163, 176 
Superior or Anterior Medullary 

109, 112 

Venous Sinuses, 51, 57 
Ventral Cochlear Nucleus, 209 
Ventricles (ventriculus, dim. of 

venter, a belly), Brain, 155 
Dissection to expose, 48 
Epithelial Lining of (Epen- 

dyma), 34, 158 
Fifth, 162 
Fourth, 119 et seq. 
Floor, 1 20 
Walls, 122 
Roof, 122 
Ependyma, 123 
Openings, 123 
Grey Matter, 124 
White Matter, 125 
Lateral, 155 
Cornua of, 157 
Communications of, 159 
Third, 159 
Verga, 177 

Vermiform Processes or Vermis 
Cerebelli, 104, 105, 107, 108 
Vesicles, Anterior Cerebral Pros- 

encephalon), 241 
Hemispherical, 242, 243 
Middle Cerebral (Mesencepha- 

lon), 240 
Posterior Cerebral (Rhomben- 

cephalon), 240 
Table of, 239 

Vesicular Columns, Anterior, 35 
Lateral, 37 
Middle, 37 



262 



INDEX 



Vesicular Columns, Posterior 
(Clarke's), 36 

Table of, 37 
Vessels of Spinal Cord, n et seq. 

of Brain, 61 et seq. 

of Cortical Centres, 143 
Vestibular Division of Auditory 

Nerve, 208 

Vestibular Nucleus, 208 
Vicq. d'Azyr, Bundle of, 176 
Vieussens, Valve of, 105, 109, 112 

Weight of Brain, 49 

W 

White Matter, Cerebellum, 109, 
116 



White Matter, Cerebrum, 171 
et seq. 

Fourth Ventricle, 125 

Medulla, 73 et seq. 

Pons Varolii, 97, 98 

Spinal Cord, 2, 20 et seq. 

Structure, 30 

Tegmentum, 185 
Willis, Circle of, 64, 66, 148 

Chordae, 58 



Zone, Mixed, 25 
Anterior Root, 22 
Marginal, Postero-Marginal, 26 
Posterior Root, 29 



J A J. GRAY, PRINTERS, EDINBURGH. 











University of Toronto 
Library 



DO NOT 

REMOVE 

THE 

CARD 

FROM 

THIS 

POCKET 



Acme Library Card Pocket 

Under Pat. "Rel. Index File" 
Made by LIBRARY BUREAU